A 56-year-old Caucasian man with non-Hodgkin's lymphoma, who had previously been treated with prolonged intensive chemotherapy, was hospitalized for an acute and reversible kidney injury of multifactorial origin. The urinary sediment examination, performed daily, demonstrated the presence of renal tubular cells and renal tubular cell casts. Surprisingly, it also showed the presence of trophozoites of the protozoan Balantidium coli, which were identified on the basis of its characteristic morphology and rapid movements across the slide, and transient leukocyturia. The patient was asymptomatic, his medical history was negative for gastrointestinal disease, and no Balantidium coli was found in the feces. In spite of this, due to the previous chemotherapy, the patient was treated with oral metrodinazole. Only one other case with Balantidium coli in the urine sediment has been described so far and this paper stresses the importance of the examination of the urinary sediment.