OBJECTIVE To determine the prevalence of aberrations in the resting electrocardiogram (ECG) in female athletes. METHODS Case-control study. METHODS Thirty female endurance athletes and 30 age-matched nonobese nonathletic control subjects. METHODS Different measurements based on resting ECGs. RESULTS The athletes had lower heart rate (mean 53 +/- SD 7) than the controls (67 +/- 11; p < 0.0001), but no group difference was found in atrioventricular conduction (PQ interval). Cornell voltage (RaVl + SV3) reflecting left ventricular mass was higher in athletes (1.18 +/- 0.58 mV vs. 0.78 +/- 0.41 mV; p = 0.0030), but the deviations from normal limits were small. The index reflecting right ventricular mass (RV1 + SV5) was higher in athletes (0.58 +/- 0.23 mV) than controls (0.45 +/- 0.23 mV; P = 0.036) but did not exceed the criterion for right side hypertrophy. QRS duration was slightly prolonged in athletes (99 +/- 10 ms vs. 92 +/- 9 ms; p = 0.010), as were rate-adjusted QT intervals (p < 0.05). J-point elevations (p = 0.0062) and ST-segment elevations (p = 0.013) were seen more frequently in athletes, but were usually small. CONCLUSIONS The female athlete's ECG differs less from control subjects than has been reported in male athletes. Extrathoracal anatomic considerations may explain some of the sex differences. However, when clear-cut ECG abnormalities are observed in female athletes, organic heart disease must be carefully excluded.