We describe 30 cases (1.7%) of community-acquired penicillin-susceptible Streptococcus agalactiae endocarditis among 1771 episodes of endocarditis diagnosed in 4 Spanish hospitals from 1975 through 1998. Endocarditis affected a native valve (most often the mitral valve) in 25 cases (83%). Surgical valve replacement was performed for 12 patients (40%). Fourteen patients (47%) died. Mortality rates for patients with native and prosthetic valve endocarditis were 36% and 100%, respectively (P=.01). The mortality rate for native valve endocarditis decreased during the last 6 years of the study (from 61% in 1975-1992 to 8% in 1993-1998; P<.05). Additionally, 115 cases in the literature from 1962-1998 were reviewed. During 1980-1998, the percentage of patients who underwent cardiac surgery increased from 24% (in the previous period, 1962-1979) to 43% (P=.05) and the mortality rate decreased from 45% to 34% (P=NS). S. agalactiae is an uncommon cause of endocarditis with a high mortality rate, although the prognosis of native valve endocarditis has improved in recent years, probably because of an increased use of cardiac surgery.