Abstract Background Our goal was to identify genetic and modifiable risk factors for upper urinary tract infections (UTIs). Methods We used data from UK Biobank, the Trøndelag Health Study, and the Michigan Genomics Initiative to conduct genome-wide association studies and sex-stratified analyses on upper UTI. Mendelian randomization (MR) analyses were conducted to examine potential causal relationships between cardiometabolic risk factors and upper UTIs. Results One genome-wide significant (P ≤ 5E-08) locus was associated with the susceptibility to upper UTI, located near TSN in the female-only analysis. Additionally, we identified suggestive (P ≤ 5E-06) loci near DNAI3 for females, SCAMP1−AS1 for males, and near TSN, LINC00603, and HLA-DQA2 for both sexes. In MR analyses, higher genetically predicted lifetime smoking scores were associated with an increased risk of developing upper UTI for females and both sexes (odds ratio [OR], 4.84, P = 4.50E-06 and OR, 2.79, P = 3.02E-05, respectively). Conclusions We found that genetic variants near TSN was associated with the risk of upper UTIs among females. In addition, we found several genetic loci with suggestive associations with the risk of upper UTIs. Finally, MR analyses found smoking to be a potential causal risk factor for upper UTIs.