Background: An estimated 5% of kidney cancers are associated with hereditary RCC syndromes. Current germline genetic testing guidelines for patients with kidney cancer were developed to identify carriers of known RCC-associated genes and have evolved in the panel-testing era. We evaluated the utility of the recent National Comprehensive Cancer Network (NCCN) recommendation of testing all patients with early-onset RCC (defined as age of diagnosis ≤ 46 years) for germline variants in genes implicated in hereditary RCC syndromes. Methods: We retrospectively identified patients with RCC diagnosed at age ≤ 46 years who underwent targeted germline testing at our institution through referral to clinical genetics service (n = 68, 29%) or through broad germline testing of ≥77 cancer susceptibility genes using next generation sequencing as part of a prospective matched tumor-normal genomic profiling initiative (n = 165, 71%). Diagnostic performance of referral criteria was assessed by the presence of pathogenic/likely pathogenic (P/LP) germline variants in RCC-associated genes and incidental cancer susceptibility genes. Results: Of 233 patients, 61% were male, 74% were Caucasian, 15% had family history of RCC, 15% had RCC-syndromic features, including 9% with multifocal renal tumors. Most patients (54%) had clear cell RCC (ccRCC). P/LP germline variants were identified in 42 (18%) patients but only 21 (9%) had mutations in RCC genes (12 FH, 4 VHL, 2 SDHB, 1 each in BAP1, TSC1, and FLCN). All 21 early-onset patients with germline variants in an RCC-associated gene also had one of the following risk factors: non-ccRCC histology, family history, or syndromic features. In 91 patients (39%) with a non-RCC germline variants or no alteration, none of these three risk factors were found. Of 21 patients with non-RCC P/LP germline variants, 9 had mutations in moderate/high penetrance genes (BRCA1 [2], ATM [2], CHEK2 [1], TP53 [2], PALB2 [1], and RET [1]); 8/9 (89%) met standard criteria for testing for those genes independent of early-onset RCC diagnosis. Conclusions: Patients with early-onset clear cell RCC and no suspicious personal or family history are unlikely to have an RCC-associated germline mutation. RCC-gene panel testing has highest utility in early-onset patients with either non-ccRCC histology, family history of RCC, or RCC-associated syndromic features. Given the high frequency of non-RCC P/LP variants, early-onset RCC patients should be counseled regarding broader testing beyond RCC-associated genes.