2-Dimensional and M-mode Echocardiography were performed in 142 fetuses at specific risk for congenital heart disease between 16 and 40 weeks of gestational age. In 105 cases the diagnosis was checked at delivery; prevalence of cardiac malformations was 5.7%. In 5 cases out of 7 the malformation was correctly diagnosed at Echocardiographic examination: ectopia cordis of thoracic type with tetralogy of Fallot, ectopia cordis of abdominal type with normal intracardiac anatomy, atrio-ventricular canal, left atrial membrane, single heart in jointed twins. There were 3 diagnostic errors: two false negative (a case of pulmonary atresia and a case of univentricular heart) and one false positive (a case of suspected transposition of the great vessels in a normal heart). The sensitivity of the test was 71.4%, the specificity was 98.9%, the predictive value of the positive test was 83.3%. M-mode Echo was particularly useful in cases of arrhythmias. 3 cases of benign rhythm disorders were identified: 2 cases of conducted and blocked atrial ectopic beats and one case of transient 2:1 A-V block. In 5 cases there was a wide variability of the sinus rhythm. 2-D Echocardiogram seems a reliable method for the diagnosis of fetal heart diseases in a population at risk. Its clinical usefulness to guide therapeutic decisions in our population was limited by the coexistence of multiple malformations.