A rare case of peritonitis due to beta-lactamase-negative, ampicillin-resistant Haemophilus influenzae is described in an 18-year-old male undergoing automated peritoneal dialysis. The infection was probably of respiratory origin. Two strains of H. influenzae cultured from peritoneal fluid and a nasal swab were indistinguishable by molecular methods. The patient was successfully treated with oral ciprofloxacin. The authors suggest that this species should be taken into account as the etiologic agent of peritoneal dialysis-associated peritonitis. Targeted antimicrobial therapy should be based on local antibiotic resistance patterns.