The association between dietary fat and fertility is not well-studied. We evaluated intakes of total fat, saturated fatty acids, monounsaturated fatty acids, polyunsaturated fatty acids, trans fatty acids (TFA), and omega-3 and-6 fatty acids in relation to fecundability in Danish and North American preconception cohort studies. Female pregnancy planners completed a validated food frequency questionnaire at baseline. Pregnancy status was updated bimonthly for 12 months or until pregnancy. Fecundability ratios (FR) and 95% confidence intervals (CI) were estimated using multivariable proportional probabilities regression. Intakes of total fat and saturated, monounsaturated, polyunsaturated, and omega-6 fatty acids were not appreciably associated with fecundability. TFA intake was associated with reduced fecundability in North America (4th vs. 1st quartiles: FR=0.86, 95% CI: 0.71, 1.04) but not Denmark (4th vs. 1st quartiles: FR=1.04, 95% CI: 0.86, 1.25), though intake in Denmark was low. In North America, omega-3 fatty acid intake was associated with higher fecundability, but there was no dose-response (among non-users of fish oil supplements: 4th vs. 1st quartiles: FR=1.40, 95% CI: 1.13, 1.73); no association was found in Denmark, where low intake was rare. In this study, high TFA intake and low omega-3 fatty acid intake were associated with reduced fecundity.