A 70-year-old male with chronic lymphocytic leukemia (CLL) 9 years ago initially presenting elevation of prostate specific antigen (PSA) was diagnosed with high-risk prostate cancer in March, 2018. He received 18F-FDG positron emission tomography/computed tomography (PET/CT), which showed mild FDG-avidity in swollen lymph nodes across the entire body, considering CLL. Then he underwent neoadjuvant androgen deprivation therapy for 1 month and then robot-assisted radical prostatectomy and biopsy of the right iliac vascular obturator lymph nodes. The prostate pathology was prostate cancer, and the pathology of lymph nodes was CLL. His serum PSA levels 1 month and 3 months after operation both reached the level of cure. For the patients with concomitant high-risk prostate cancer and CLL, PET/CT may be valuable in distinguishing whether the swollen lymph nodes were infiltratedprostate cancer and guiding the lymphadenectomy. [Key words]prostate neoplasm; chronic lymphocytic leukemia; positron emission tomography/computed tomography; lymphadenectomy