Secondary peritonitis is a common and serious form of intra-abdominal infection, often associated with high morbidity and mortality. The overall patient outcome has not markedly improved in spite of advances in patient management. There is therefore need to study the pattern of bacterial pathogens associated with secondary peritonitis in Lagos University Teaching Hospital (LUTH) and the antibiotic susceptibility pattern as that would help in formulation of empiric antibiotic policy on peritonitis and improve the outcome/prognosis of the patients. A prospective study of 35 patients with suspected peritonitis at LUTH between February, 2002 and June 2003 was done. Peritoneal fluids of these patients were collected intra-operatively under aseptic conditions. The specimens were subjected to aerobic and anaerobic studies. Twenty-seven isolates were identified aerobically with Escherichia coli being the most predominant organism 11 (31.4%) followed by Staphylococcus aureus 6 (17.1%) then Klebsiella spp 4 (11.4%). Anaerobic culture showed Prevotella species as the most predominant 14 (40%) followed by Bacteroides fragilis group 8 (22.9%). Overall, Prevotella species were the most predominant organisms isolated in LUTH patients with secondary peritonitis.