Two different series of patients with Infectious Endocarditis (IE), hospitalized in the same ward of Curry Cabral Hospital in Lisbon, are presented and compared. The two series were separated by a ten-year period--the first included patients observed from 1970 to 1976 and the second from 1988 to 1998. In the first series (20 patients), IE occurred mainly in patients with previous cardiac valvular lesion, the course was subacute and Streptococcus viridans was the predominant agent. In the last series (65 patients), most of the patients were young and had no previous valvular lesions. Right side endocarditis predominated and the course was acute. Most of patients were drug addicts and had HIV infection. Staphylococcus aureus was the predominant agent. The ages of the two series were significantly different (p < 0.005). The diagnostic value of transthoracic and transesophageal echocardiography is stressed. The details of the evolution of patients with HIV infection are presented according to the values of CD4+ lymphocyte counts. The relatively good prognosis of IE in drug addicts with antibiotic treatment, even with HIV infection, is emphasized.