The records of height of 22841 18-year-old Portuguese males were analysed as well as their parents educational level and localities of subject's residence (districts). The sample includes all the Portuguese 18-year-old males, born in 1978 and examined in 1996, in central and southern Portugal, representing all the social strata. Statistically significant differences (p < or = 0.001) among the districts were found: males from Setúbal (172.75 cm) and Lisboa (172.64 cm), the most developed districts, are the tallest, and those from C. Branco (170.79cm) and Coimbra (171.19 cm) are the shortest. Comparing to published data from 1904, a positive secular trend in height was found. The average increase was 8.99 cm, which yields a rate of 0.99 cm per decade. This positive trend must be related to the general improvement in the population's standard living conditions, as the striking drop of post-neonatal mortality rate shows after the 1960s and 1970s. Despite this positive trend, great social difference still exists: the gap between the two extremes of parents' educational level is almost 4 cm for height. Analysis of variance (ANOVA) showed significant effects of father's and mother's educational level as well as subject's locality of residence, but the influence of parents' educational level was stronger than that of geographic residence. These results suggest that the secular trend in height will continue for the Portuguese population in the future decade.