Echocardiographic follow-up of left ventricular (LV) volumes is difficult because of the test–retest variation of 2-dimensional echocardiography (2DE). We investigated whether the accuracy and reproducibility of real-time 3-dimensional echocardiography (RT3DE) would make this modality more feasible for serial follow-up of LV measurements. We performed 2DE and RT3DE and cardiac magnetic resonance imaging (MRI) in 50 patients with previous infarction and varying degrees of LV function (44 men; 61 ± 11 years of age) at baseline and after 1-year follow-up. Images were obtained during breath-hold and measurements of LV volumes and ejection fraction were made offline. Over follow-up, end-diastolic volume decreased from 192 ± 53 to 187 ± 60 ml (p <0.01), end-systolic volume decreased from 104 ± 51 to 95 ± 53 ml (p <0.01), and ejection fraction increased from 48 ± 12% to 51 ± 12% (p <0.01). MRI showed that LV mass shrank from 183 ± 39 to 182 ± 37 g (p <0.01). The correlation between change in RT3DE and change in MRI was greater than the correlations of 2DE with MRI for measurement of end-diastolic volume (r = 0.47 vs 0.02, p <0.01), end-systolic volume (r = 0.44 vs 0.17, p <0.01), and ejection fraction (r = 0.58 vs −0.03, p <0.01). The change in end-diastolic volume between baseline and follow-up with RT3DE (−4 ± 20, p <0.01) was similar to that with MRI but was unrecognized by 2DE (4 ± 19, p = 0.09). There was good test–retest and inter- and intraobserver correlation within RT3DE for volumes, ejection fraction, and mass. In conclusion, if sequential measurement of LV volumes is used to guide management decisions, 3DE appears preferable to 2DE.