A 25-year-old male was hospitalized for diarrhea and weight loss. Since childhood he had experienced recurrent episodes of pneumonia and diarrhea. Physical and laboratory findings were compatible with malabsorption. On endoscopy, nodular lymphoid hyperplasia (NLH) of the small intestine was found. Common variable immunodeficiency syndrome (CVID) was suspected and diagnosis was established by demonstrating a significant reduction of plasma gamma-globulin levels. Immediately after starting immunoglobulin treatment diarrhea stopped, and both incidence and severity of pulmonary infections were significantly reduced, while recurrent gastrointestinal infections (notably lambliasis and Campylobacter infections) continued to occur and both bronchiectases and splenomegaly were progressive over years. This case report focuses on CVID as a potential underlying cause of diarrhea. The most important complications of the disease are presented. Therapeutical options are discussed in the light of recently published data.