Rhabdomyosarcomas are the most common soft tissue sarcomas in children. Here we present management of an 18-month-old boy with metastatic rhabdomyosarcoma of the bladder/prostate. After radiochemotherapy, high-spatial-resolution 3-Tesla multiparametric magnetic resonance imaging (MRI) showed regressive systemic disease but a residual mass at the right seminal vesicle. For histologic re-evaluation, 3-dimensional-controlled stereotactic MRI/transrectal ultrasound (TRUS)-fusion biopsy specimens were taken. Because histologic analysis showed nonvital tissue, a decision could be made against adjuvant radical cystoprostatectomy. Advanced 3-Tesla imaging and MRI/TRUS-fusion biopsies in children are feasible and represent an effective tool to examine suspicious pelvic lesions. Depending on histology, this can lead to a significant reduction of therapy-associated morbidity.