Twenty-five neonates (16 boys and 9 girls) who had atrial flutter were identified. Diagnosis was made on or before the first day of life in 18 (72%). Heart failure was present in 9 patients, and hydrops fetalis was present in another 5. Atrial and ventricular rates did not differ between symptomatic and asymptomatic patients. Atrioventricular conduction was variable in 16 patients, and documented 1:1 conduction occurred in 5. Digoxin was the initial drug therapy given to 21 patients, with 7 reverting to sinus rhythm. Electrical cardioversion (pacing or synchronized shock) was attempted in 13 of the 14 cases in which digoxin was not successful and was attempted as the first treatment in 3 cases. Sustained sinus rhythm was achieved in 9. Two infants died of complications from prematurity but without having been successfully converted to sinus rhythm. No patient had atrial flutter during long-term follow-up (median 23 months). Neonatal atrial flutter has significant morbidity but an excellent long-term prognosis. (Am Heart J 1997;133:302-6.)