ABSTRACT Univariate and multivariate statistical analyses of 28 meristic characters recorded for 19 samples of the lizard Liolaemus monticola monticola were used to compare geographical variation in morphology with chromosomal races north and south of the Maipo River, and north and south of the Aconcagua River in central Chile, plus some affluent. This extends a previous morphological study that confirmed that the Maipo River is a biogeographical barrier that separates chromosomal races "Southern, 2n=34" and "Northern, 2n=38-40", and reports for the first time the importance of the Aconcagua River as another biogeographical barrier between the chromosomal races "Northern, 2n=38-40" and the "Multiple Fission, 2n=42-44". The phenetic variation among samples is sufficient to differentiate the three chromosomal races, and also distinguishes populations within the chromosomal races such as the ones separated by the Colorado River, an affluent of the Aconcagua River. A possible historical sequence of events that accounts for the pattern of morphological differentiation is advanced.