Hydrogel spacers can be inserted to create a gap between the prostate and rectum prior to radiotherapy for prostate cancer, enabling higher radiation doses while reducing rectal toxicity. Spacer infection is relatively rare but significant. We report a case of robot-assisted radical prostatectomy performed for spacer infection and prostate cancer. A 75-year-old man with a hydrogel spacer presented with fatigue and fever after completing 30 Gy of radiation therapy for prostate cancer. He was diagnosed with a periprostatic abscess associated with the hydrogel spacer. Following antibiotic treatment, he underwent robot-assisted radical prostatectomy with concurrent abscess drainage. The treatment outcome was favorable. This case of a radical prostatectomy conducted for spacer infection represents, to our knowledge, the first documented case of management of a hydrogel spacer infection. The favorable treatment outcome suggests that this may be a viable treatment option for similar cases.