To investigate a possible effect of reduced fecundability (probability of conception per menstrual cycle) among women who fabricate silicon wafers, 152 fabrication-room (fab) and 251 nonfab workers were followed for an average of five menstrual cycles. Daily urine samples were analyzed to confirm clinical spontaneous abortions (SABs) and early fetal losses (EFLs). Adjusted fecundability odds ratios (FRs) for fab workers ranged from 0.59 to 0.72 (p = 0.09-0.28 vs. nonfab). For clinical pregnancies only, the adjusted FR ranged from 0.43-0.50 (p = 0.04-0.09 vs. nonfab). This lower fecundability was most pronounced among dopants and thin-film workers [adjusted FR = 0.61, 95% confidence interval (CI) = 0.27-1.40 for all pregnancies; adjusted FR = 0.22, 95% CI = 0.05-0.96 for clinical pregnancies] and in workers exposed to ethylene-based glycol ethers (adjusted FR = 0.37, 95% CI = 0.11-1.19).