(1) Describe gestational diabetes mellitus (GDM) prevalence time trends in USborn (USWH) and Mexico-born (MWH), white Hispanic Colorado women and (2) Determine effect of maternal birthplace on GDM prevalence. Retrospective population-based study of 1995-2004 Colorado birth certificate data for live, singleton births to white, Hispanic mothers estimated prevalence, trends, and association of GDM and maternal birthplace. Univariate, bivariate and logistic regression analyses were conducted. GDM prevalence in 154,957 births increased in both USWH (1.77-2.53%, P < 0.0001) and MWH (2.38-3.08%, P < 0.0001). Over study years, MWH had higher crude odds (OR = 1.30; 95% CI = 1.22-1.38) for developing GDM than USWH. Adjustment for maternal age and maternal education reduced GDM risk by birth country (OR = 1.05; 95% CI = 0.98-1.13, P = ns). GDM prevalence increased in both US-born and Mexico-born, white, Hispanic Colorado women. Mexico-born immigrant women may have increased risk for GDM compared with their USborn counterparts. Lower education attainment may be determinant of disease risk.