The aim was to determine if selenium supplementation during pregnancy reduces the occurrence of premature (pre-labour) rupture of membranes (PROM). A total of 166 primigravid pregnant women in the first trimester of pregnancy, were randomised to receive 100 microg of selenium (n = 83, drop-outs = 22) or a placebo (n = 83, drop-outs = 19) per day until delivery. The incidence of PROM, as well as serum selenium concentrations were evaluated at baseline and at the end of the study. Supplementation with selenium was associated with a significant increase in mean serum selenium concentration at term (p < 0.001). In contrast, mean serum selenium concentration remained unchanged in the control group (p > 0.05). The incidence of PROM was significantly lower in the selenium group (n = 8, 13.1%) than in the control group (n = 22, 34.4%) (p < 0.01). Our findings indicate that selenium supplementation (100 microg/day) in pregnant women effectively reduces the incidence of PROM.