In México, 44 thousand hectares are planted with tomatillo or husk tomato (Physalis philadelphica Lam.), which occupies fourth place among the country’s vegetable species. However, research on this species is scarce, especially that related to the process of seed deterioration. We studied the effects of deterioration in tomatillo seed, var. CHF1-Chapingo, stored from 2-mo up to 7 yr with no climate control, 18.2 ± 5 °C and 41 ± 10% relative humidity, on physiological and biochemical variables during germination. It was found that germination, vigor, and respiratory activity decrease significantly from the first year of storage; thus, after 7 yr, germination and vigor decreased 99%, and respiratory activity of seed after 48 h imbibition decreased 78%. Linoleic acid (unsaturated) content correlated positively with germination (R = 0.78**) and with speed of radicle emergence (R = 0.79**). Germination correlated with speed of radicle emergence (R = 0.99**) and with respiratory activity after 48 h of imbibition (R = 0.79**). Both respiratory activity and fatty acid content are involved in natural deterioration of tomatillo seed.