Celiac disease is the most common severe food intolerance in the Western world and is due to gluten ingestion in genetically susceptible children and adults. The key treatment in these patients is a gluten-free diet, because most complications are more common when dietary compliance is poor. The most serious complication of celiac disease is the development of neoplasms (the most common of which is enteropathy-associated T-cell lymphoma). However, a number of reports have indicated an increased prevalence of ulcerative jejunitis and extraintestinal manifestations, including chronic hepatitis, fibrosing lung disease, and epilepsy syndromes. We report the case of a 53-year-old-man with long-standing diarrhea; because celiac disease was not suspected, the patient developed celiac-associated T-cell lymphoma and mesenteric panniculitis.