The hypothesis that independently of sex, brain volume (BV) and head circumference (HC) are positively and significantly associated with intellectual quotient (IQ) was examined in a sample of 96 high school graduates of high [Wechsler Intelligence Scale for Adults--Revised (WAIS-R) is greater than 120] and low IQ (WAIS-R is less than 100) (1:1), from high and low socioeconomic stratum (SES), and of both sexes (1:1) from the Chile's metropolitan region. Brain development was assessed by magnetic resonance imaging (MRI) and anthropometric measurements were made applying standardized procedures. Results showed that, in general, no significant differences were observed between absolute and adjusted brain parameters by body size. Differences in BV and HC can be more properly attributed to differences in IQ and not to SES both in males and females. Independently of sex, BV was the only brain parameter that contributed to explain IQ variance. These findings confirm the hypothesis that independently of sex, BV and HC are positively and significantly associated with IQ.