Objective. Poststreptococcal reactive arthritis (ReA) is a (poly)arthritis presenting after a Streptococcus group A infection. Acute rheumatic fever (ARF), albeit caused by the same pathogen, has different risk characteristics and is considered to be a separate entity. Whereas ARF is known to cause carditis, the risk of carditis in adult poststreptococcal ReA is unknown. Consequently, the prevailing recommendations regarding long-term antibiotic prophylaxis in poststreptococcal ReA are imprecise and derived from the data on ARF. This study was undertaken to investigate the development of valvular heart disease in an unselected cohort of adult patients with poststreptococcal ReA who did not receive antibiotic prophylaxis and were followed up prospectively.Methods. All patients presenting with early arthritis to an inception cohort of >2,000 white patients were evaluated. Patients presenting with poststreptococcal ReA (n ؍ 75) were selected. After a median followup of 8.9 years, the occurrence of valvular heart disease was evaluated by transthoracic echocardiography in 60 patients. Controls were matched for age, sex, body surface area, and left ventricular function, with a patient-tocontrol ratio of 1:2.Results. No differences were seen in left ventricular dimensions. Morphologic abnormalities of the mitral or aortic valves were not more prevalent among patients than among controls. Mild mitral regurgitation was present in 23% and 21% of patients and controls, respectively. Mild aortic regurgitation was present in 10% and 11%, and mild tricuspid regurgitation in 43% and 39%, respectively, revealing no significant differences.Conclusion. Our findings indicate that there is no increased risk of valvular heart disease in adult poststreptococcal ReA. Based on these data, routine longterm antibiotic prophylaxis is not recommended in adult poststreptococcal ReA.