Hypothyroidism has been associated with dyslipidemia. Its treatment with levothyroxine has shown a positive effect on the lipid profile in adults, however, there is a lack of data on the pediatric population.Objective: to evaluate the effect of the thyroid profile normalization on the lipid profile in children with primary hypothyroidism.Patients and Method: Retrospective study in children aged from 6 to 16 years, with diagnosis of primary hypothyroidism due to Hashimoto’s thyroiditis, in treatment with levothyroxine, and who had an evaluation of serum lipids before and during their treatment. The lipid profile was evaluated in 2 stages: the first one referred to as “before levothyroxine treatment” (at the diagnosis of primary hypothyroidism) and the second one referred to as “ thyroid profile normalization” (when normalization of Thyroid-stimulating hormone [TSH] and free T4 [FT4] was achieved during levothyroxine treatment). Sociodemographic and anthropometric data were recorded. The lipid profile evaluation consisted of the serum determination of total cholesterol (TC), high-density cholesterol (HDL-C), and TG. The phenotype of dyslipidemias was determined according to the Fredrickson’s classification.Results: 72 patients were included (61% women; age 11.5 ± 2.9 years), out of which 58.3% (n = 42) presented pre-treatment dyslipidemia. In hypothyroid state, it was evident the correlation of TSH with TC (r = 0.36; p = 0.002), LDL-C (r = 0.46; p = 0.01), and HDL-C (r = -0.33; p = 0.004). The thyroid profile normalization showed the reduction of TC [184 mg/dL (IQR 92-322) vs 147 mg/dL (IQR 92-283); p = 0.05], LDL-C [99 mg/dL (IQR 44-232) vs 82 mg/dL (IQR 41-168); p = 0.02], TG [113 mg/dL (IQR 50-483) vs 88 mg/dL (IQR 16-343); p = 0.03], and the frequency of dyslipidemia [58.3% vs 22.2%; p = 0.001), as well as the TC correction with TG (r = 0.35; p = 0.02) and LDL-C (r = 0.88; p = 0.01). Persistent dyslipidemia was associated with obesity (r = 0.27; p = 0.02), overweight (r = 0.58; p = 0.001), and pre-treatment dyslipidemia (r = 0.53; p = 0.001).Conclusions: There is an association between TSH, TC, LDL-C, and HDL-C in hypothyroidism. When the thyroid profile was normalized, there was a reduction of TC, TG, LDLC, and dyslipidemia frequency. Persistent dyslipidemia was associated with obesity, overweight, and pre-treatment dyslipidemia.El hipotiroidismo ha sido asociado con dislipidemia. Su tratamiento con levotiroxina ha mostrado un efecto positivo sobre el perfil lipídico en adultos, siendo poco descrito en población pediátrica.Objetivo: Evaluar el efecto de la normalización del perfil tiroideo sobre el perfil lipídico en niños con hipotiroidismo primario.Pacientes y Método: Estudio retrospectivo en niños de 6 a 16 años de edad, con diagnóstico de hipotiroidismo primario por tiroiditis de Hashimoto, en tratamiento con levotiroxina, y que contaron con evaluación de lípidos séricos antes y durante su tratamiento. Se evaluó el perfil lipídico en 2 tiempos: el primero, referido como “antes del tratamiento con levotiroxina” (al diagnóstico de hipotiroidismo primario) y el segundo, referido como “a la normalización del perfil tiroideo”. Se registraron datos sociodemográficos y antropométricos. La evaluación del perfil lipídico consistió en la determinación sérica de colesterol total (CT), colesterol de alta densidad (HDL-C) y TG. El fenotipo de las dislipidemias se caracterizó a través de la clasificación de Fredrickson.Resultados: Se incluyeron 72 pacientes (61% mujeres; edad de 11,5 ± 2,9 años), de los cuales 58,3% (n = 42) presentó dislipidemia pretratamiento. En estado hipotiroideo, se evidenció la correlación de TSH con CT (r = 0,36; p = 0,002), LDL-C (r = 0,46; p = 0,01) y HDL-C (r = -0,33; p = 0,004). A la normalización del perfil tiroideo se evidenció la reducción de CT [184 mg/dL (RIC 92-322) vs 147 mg/dL (RIC 92-283); p = 0,05], LDL-C [99 mg/dL (RIC 44-232) vs 82 mg/dL (RIC 41-168); p = 0,02], TG [113 mg/dL (RIC 50-483) vs 88 mg/dL (RIC 16-343); p = 0,03] y de la frecuencia de dislipidemia [58,3% vs 22,2%; p = 0,001), así como la corrección de CT con TG (r = 0,35; p = 0,02) y LDL-C (r = 0,88; p = 0,01). La persistencia de dislipidemia se asoció con obesidad (r = 0,27; p = 0,02), sobrepeso (r = 0,58; p = 0,001) y dislipidemia pretratamiento (r = 0,53; p = 0,001).Conclusiones: Existe una asociación entre TSH, CT, LDL-C y HDL-C en hipotiroidismo. Al normalizarse el perfil tiroideo, se evidenció una reducción de CT, TG, LDL-C y frecuencia de dislipidemia. La dislipidemia persistente post-tratamiento se asoció con obesidad, sobrepeso y dislipidemia pretratamiento.