Isospora belli infection is frequent in immunosuppressed patients and can cause wasting diarrhea. We present the first isosporiosis case in a renal transplant recipient from Turkey. The 25-year old male patient who had had a renal transplantation due to renal failure and had received immunosuppressive therapy presented at the hospital complaining of weakness, nausea, vomiting and diarrhea that had lasted for 15 days. Isospora belli oocysts were detected in stool samples by direct microscopy, modified Ziehl-Neelsen staining methods and autofluorescence technique. Oocysts in the stool samples were also sporulated in 2.5% potassium dichromate and the sporulated oocysts were seen microscopically. The patient was treated with co-trimoxazole (trimethoprim 160 mg, sulphamethoxazole 800 mg) every 12 hours for seven days, with elimination of the symptoms at this time. After this, Isospora belli oocysts were no longer seen in stool samples.