Hereditary leiomyomatosis and renal cell cancer (HLRCC) is caused by heterozygous germline mutations in the fumarate hydratase (FH) gene and is associated with increased susceptibility to cutaneous leiomyomas, uterine leiomyomas, and renal cell carcinoma (RCC). This report describes a seven-year-old male who developed a large right kidney tumor with multiple cystic lesions that contained enhanced solid components. Whole-exome sequencing identified his germline mutation in the FH gene and its loss of heterozygosity in the tumor. This was the youngest-onset case of HLRCC-associated RCC to date. This report may affect the starting age for future RCC-surveillance programs for patients with HLRCC.