The paper describes a 56-year-old female patient who in December 2015 lost her appetite and 20 kg of weight, had diarrhea, rapidly increasing weakness, dizziness, joint pains, fever, swelling of the feet, and convulsions. Blood tests revealed anemia, elevated erythrocyte sedimentation rate, and hypoproteinemia. Computed tomography showed enlarged mesenteric and retroperitoneal lymph nodes. The doctor suspected lymphoma and referred her to the Moscow Clinical Research Center. The diagnosis of Whipple’s disease was established by carrying out a small intestinal (duodenal) mucosal biopsy with the PAS reaction. A fat-free diet and antibiotic therapy with co-trimoxazole 2.0 g/day and ciprolen 0.3 g/day were prescribed for the patient. Fever and diarrhea disappeared, appetite appeared, weight gained, and blood counts normalized over 1 month of treatment. The patient was discharged with a recommendation to continue antibiotic treatment until the histopathological signs of the disease ceased.