A retrospective survey of patients with pneumococcal infective endocarditis at the University Hospital, Leiden, over a 10-year period (1976-1986) yielded five cases. Applying strict case definitions, four patients had definite and one patient possible pneumococcal endocarditis. The commonest presenting signs and symptoms were malaise, fever, and congestive heart failure. Predisposing conditions were previous splenectomy in one case and a valve prosthesis in another. The aortic valve was the most common site of infection. In four of the five patients the diagnosis of endocarditis was made during life. These patients were treated appropriately, i.e. with antibiotics to which S. pneumoniae is sensitive. In three patients, surgical intervention was performed in the acute phase because of progressive heart failure. Paravalvular abscesses were observed at surgery in all these cases. The four patients treated in our series recovered fully; the single fatal case constituted an unrecognized case of pneumococcal endocarditis. If recognized and treated appropriately (particularly with early selective surgery) endocarditis can be cured. In a statistical analysis of 36 patients with pneumococcal endocarditis reported during the past five years, we found a significantly higher occurrence and mortality in men than in women; no other clinical features were associated with a poor outcome of illness.