BACKGROUND Surgical acute abdomen is one of the commonest causes of admission into the surgical emergency room. It is a sudden onset of abdominal disease condition which requires immediate surgical evaluation and intervention. AIM To determine the pattern and outcome in surgical acute abdomen and compare pre-operative diagnosis with intra-operative diagnosis. METHODS This was a prospective descriptive study done at University of Benin Teaching Hospital, Benin over one year period between September 2009 and August 2010. Consecutive patients aged 18years and above with diagnosis of surgical acute abdomen formed the study sample. Patients whose surgical acute abdomen was caused by gynaecological and urological problems were excluded. A data form was opened for all patients at presentation. Patients who met the inclusion criteria were recruited into the study. Data collated from the patients’ Pro forma were subsequently analyzed. RESULTS One hundred and eighty-six patients who met the inclusion criteria were recruited. There were 99 males and 87 females with male to female ratio of 1.1: 1. The mean age of the patients was 36.60 ± 16.74 years with age range of 18-92 years. Acute appendicitis confirmed on histopathology in 71 patients was the commonest cause of surgical acute abdomen in the study. One hundred and seventy-four patients were treated and discharged while 12 patients died. The overall mortality rate was 6.5%. Conclusion: This prospective descriptive study has shown that acute appendicitis is the commonest cause of surgical acute abdomen at the University of Benin Teaching hospital, Benin and the 21-30 years age group was most commonly affected.