OBJECTIVE:To determine the impact of oil-based versus water-based contrast on pregnancy and live birth rates ≤5 years after hysterosalpingography (HSG) in infertile women. DESIGN:A 5-year follow-up study of a multicenter randomized trial. SETTING:Hospitals. PATIENT(S):Infertile women with an ovulatory cycle, 18-39 years of age, and having a low risk of tubal pathology. INTERVENTION(S):Use of oil-based versus water-based contrast during HSG. MAIN OUTCOME MEASURE(S):Ongoing pregnancy, live births, time to ongoing pregnancy, second ongoing pregnancy. RESULT(S):A total of 1,119 women were randomly assigned to HSG with oil-based contrast (n = 557) or water-based contrast (n = 562). After 5 years, 444 of 555 women in the oil group (80.0%) and 419 of 559 women in the water group (75.0%) had an ongoing pregnancy (relative risk [RR] 1.07; 95% confidence interval [CI] 1.00-1.14), and 415 of 555 women in the oil group (74.8%) and 376 of 559 women in the water group (67.3%) had live births (RR 1.11; 95% CI 1.03-1.20). In the oil group, 228 pregnancies (41.1%) were conceived naturally versus 194 (34.7%) pregnancies in the water group (RR 1.18; 95% CI 1.02-1.38). The time to ongoing pregnancy was significantly shorter in the oil group versus the water group (10.0 vs. 13.7 months; hazard ratio, 1.25; 95% CI 1.09-1.43). No difference was found in the occurrence of a second ongoing pregnancy. CONCLUSION(S):During a 5-year time frame, ongoing pregnancy and live birth rates are higher after tubal flushing with oil-based contrast during HSG compared with water-based contrast. More pregnancies are naturally conceived and time to ongoing pregnancy is shorter after HSG with oil-based contrast. CLINICAL TRIAL REGISTRATION NUMBER:Netherlands Trial Register (NTR) 3270 and NTR6577(www.trialregister.nl).