A nine-month-old boy consulted for intense perianal erythema. An initial rectal smear was performed with a negative result of the rapid streptococcal antigen detection test after 24 hours, so treatment was started with clotrimazole. As the patient did not progress well, it was decided to repeat the rectal and pharyngotonsillar smear, finding a positive result for rapid detection of streptococcal antigen in the rectal sample and negative in the pharyngotonsillar sample. Culture of the rectal specimen was negative for fungi and showed growth of GABHS. Treatment with oral penicillin was started for 10 days, with resolution of the picture.