BACKGROUND Malignant tumours of the gastro-intestinal tract are not as rare as previous studies suggest. Recent studies have indicated increasing incidence. OBJECTIVE To document the pattern, age and sex distribution as well as histopathology characteristics of malignant tumours of the gastro-intestinal system in Lagos and Sagamu in Southwestern Nigeria. METHODS The paraffin embedded blocks and slides as well as pathology reports of malignant tumours of the gastrointestinal (GIT) organs collected from five laboratories (Morbid Anatomy Departments of the Lagos University Teaching Hospital and Olabisi Onabanjo University Teaching Hospital in Sagamu, Ogun State as well as the three private histolopathology laboratories in Lagos State) were reviewed. The clinical data such as the age, sex, and clinical summary were extracted from the records. RESULTS About 80% (578 cases) of all the 713 malignant GIT tumours were epithelial; sarcomas, carcinoid and non-Hodgkin's lymphoma being less common. The ages ranged from 4-96 yrs (mean of 48.9 years) with the peak in patients 60-69-year age group and M:F ratio of 1.35:1. Colorectal tumours topped the list with 402 cases (56%), followed by liver 105 (14.7%), stomach 85 (12%) and omental metastases 67 (9.4%). The oesophagus, pancreas, small intestine and gall bladder represented 18 (2.5%), 16 (2.2%), 12 (1.7%), and eight (1.1%) respectively. Colorectal cancers peaked in the 60-69 year age group, liver and stomach cancer occurred mostly between the 50-59 years age group. Over half of the colorectal adenocarcinomata were located in the ano-rectum with 93 (23%) occurring in those below 40 years of age. CONCLUSION Colorectal cancer remains the commonest GIT tumour in the region. Molecular studies are imperative to identify the common subtypes of GIT tumours in order to ascertain their specific pathogenetic and prognostic features.