Most common bacterial species causing peritonitis in the course of peritoneal dialysis (PDP) are coagulase-negative staphylococci, Staphylococcus aureus and streptococci. Haemophilus influenzae is rarely associated with PDP. Hereby we present the first known case of APD-associated peritonitis caused by non-type able H. influenzae (NTHi) presenting the beta-lactamase negative, ampicillin-resistant (BLNAR) phenotype. An 18 year old boy who had been treated with the APD for 12 months due to SLE was admitted in good general condition with diagnosis of PDP. Standard diagnostic and therapeutical procedures were initiated. Dialysis fluid was turbid with cytosis of 435 WBC/ml. From dialysis fluid pure culture of Gram-negative coccobacillus was isolated. The isolate was identified as a BLNAR phenotype. The same bacterium was isolated from nasal swab. Blood cultures were negative. After evaluation of antimicrobial susceptibility the treatment was changed for the oral ciprofloxacin. The treatment was successful. Control tests 2 days later revealed cytosis of 15 WBC/mm3 and control cultures of peritoneal fluid were negative. After two weeks of treatment the patient was discharged in a good condition. Haemophilus influenzae is a bacterium frequently colonizing the nasopharyngeal cavity. A PCR-based method allowed to classify isolates as NTHi. Infection was probably of the respiratory origin as the isolates (from peritoneal fluid and nasal swab) were undistinguishable. There are only few reports describing this species as an ethiologic agent of peritonitis. This case prove that Haemophilus species should be taken into account as a possible aethiologic agent of PDP, especially in patients on immunosupression with carrier state of H. influenzae in the upper respiratory tract. This kind of microorganism requires specific conditions during its growing in vitro. Identification of its sensitivity to antibiotics is essential in order to detect strains of BLNAR phenotype, as it is a crucial part of an effective antibiotic therapy.