Whipple's disease is a rare multisystemic infectious disorder affecting predominantly middle-aged men. Clinical manifestations are very variable with a very long, insidious, prediagnostic course. Weight loss, chronic diarrhea, arthralgias, and low-grade fever are characteristic features in most patients. Although gastrointestinal compromise is very common, atypical clinical forms are being increasingly recognized. Although a bacterial cause was strongly suggested for many years, the infectious agent was elusive until recently. The bacillus that was classified as an actinomycete was named Tropheryma whipplei and has singular characteristics. It presents affinity for the periodic acid-Schiff stain, but it is negative for Ziehl-Neelsen staining and has a characteristic trilamellar cell wall. Its genetic material has been recently sequenced, and culture was finally performed on a human fibroblast cell line. Pathological specimens show macrophage infiltration with mostly intracellular invasion of live bacteria. Immunologic factors, such as a subtle defect of cellular immunity possibly specific for the Whipple's bacterium, are believed to play a role in pathogenesis. The diagnosis requires the histologic assessment of diseased tissue, showing the characteristic infiltration, as a first approach, and confirmatory tests such as electron microscopy and/or polymerase chain reaction. Antibiotic treatment is mandatory and leads to a rapid clinical improvement and remission in most patients. Although the rationale for treatment is largely empiric, current recommendations include a 2-week parenteral therapy (third generation cephalosporin) followed by a long-term therapy with trimethoprim-sulphamethoxazole. This approach has been shown to reduce the number of relapses and was effective for prevention and/or treatment of the neurologic compromise.