Sex and age differences in the incidence of hypertension and blood pressure (BP) levels and their concomitants are examined among the Manus of Papua New Guinea in the context of modernization. For Manus men, BP increases directly with both degree of modernization and duration of migration to the local towns and larger cities of Papua New Guinea, accompanied by similar increases in body mass and subcutaneous fat. For Manus women, however, although body mass and fatness increase along the modernization continuum, BP does not. Risk for hypertension (140/90 mm Hg) was increased fourfold among men who resided in town (adjusted odds ratio [AOR] = 4.4, 95% confidence interval [CI] 1.5–13.2) and also among those who were in the highest tertile of fatness (AOR = 4.1, 95% CI 1.6–10.4). Among women, older age (≥45) alone significantly increased risk tenfold (AOR = 10.5, 95% CI 1.7–66.8). Using a Mantel-Haenszel χ2, a meta-analysis of sex and age differences in relative risk for hypertension (160/95 mm Hg) among 20 Pacific populations, 9 traditional living and 11 undergoing modernization, was performed. While young men showed increased risk in modernizing populations (summary relative risk [SRR] = 1.34, 95% CI 1.12–1.60), older men had significantly reduced risk for hypertension compared with women in both traditional (SRR = 0.46, 95% CI 0.33–0.64) and modernizing groups (SRR = 0.70, 95% CI 0.59–0.84). This crossover between the sexes with advancing age is also evident for BP levels in a larger sample of societies and suggests a biological basis for hypertension risk. © 1995 Wiley-Liss, Inc.