Introduction Postoperative pyrexia is a common complication seen in surgical wards. This may be seen within a few hours after surgery or may be delayed for up to days or weeks. A close monitoring of postoperative patients is very crucial in order to diagnose pyrexia promptly in the postoperative period and treat it aggressively to decrease morbidity and mortality as well as the cost of care. Aims and Objectives The specific aim of this study was to determine the aetiology and pattern of postoperative pyrexia at the Olabisi Onabanjo University Teaching Hospital, Sagamu. This will help in early diagnosis and prompt treatment of patients who develop postoperative pyrexia. Methods This study was a prospective descriptive hospital-based study conducted on all general surgery patients from the age of 14 years and above. A proforma was administered on interview basis to collect participant’s socio-demographic data and medical history preoperatively. Postoperatively, patients’ temperatures were monitored six hourly until discharged. Clinical examinations and relevant diagnostic investigations were carried out. Pyretic patients were further evaluated based on history, targeted and specific investigations and treated accordingly. Results A total of 316 patients were managed during the period of study but only 275 patients met the criteria for inclusion. Their mean age was 39.5years (SD) (±16.77). The male to female ratio was 1:1.4. Postoperative pyrexia was more common after 48 hours of surgery. The incidence of postoperative pyrexia was 33.1%. Malaria was the commonest cause of postoperative pyrexia followed by respiratory tract infections. Two hundred and seventy-one patients were successfully managed and discharged during the study. Conclusion Patients’ evaluation is essential to diagnose the cause of postoperative pyrexia. The high incidence of postoperative pyrexia and the attendant morbidity and mortality are a major concern in this environment. Recommendation for chemophylactic treatment of patients with positive preoperative malaria test and those undergoing elective surgeries is recommended.