Perianal streptococcal dermatitis (PSD) is a superficial bacterial infection usually with group A beta-hemolytic streptococci. PSD is often misdiagnosed for long periods and patients are subjected to treatments for a variety of differential diagnoses without success. We report a 4-year-old boy with PSD who presented to our clinic with guttate psoriasis for 2 reasons: first, to make dermatologists aware of PSD and second, to emphasize the necessity to examine patients, particularly pediatric patients, with guttate psoriasis very thoroughly and swab both the pharynx and perianal and/or perigenital areas even when they are, or seem to be, asymptomatic for bacterial infections. Once PSD has been diagnosed, systemic antibiotic therapy with penicillin, erythromycin, roxithromycin, or azithromycin (probably augmented by topical mupirocin ointment) should be the treatment of choice. Therapy should be monitored by posttreatment perianal and throat swabs as well as a urine analysis to monitor for poststreptococcal glomerulonephritis. (J Am Acad Dermatol 2000;42:885-7.)