Background: Quality of life (QoL) is crucial for young adults with posterior urethral valves (PUV). This study investigates the impact of lower urinary tract symptoms (LUTS) on their quality of life and sexual health, including self-efficacy. Methods: Patients aged 16 and older treated for PUV completed four validated questionnaires (Sexual Self-Efficacy Scale (SSES-E), ICIQ MLUTS, ICIQ MLUTSsex, ICIQ LUTSqol) and an individual health questionnaire. Results: Eighteen (52.9%) patients responded, with a median age of 23 years (IQR 18–26). Three had terminal renal failure; two were transplanted. Thirteen urinated naturally; five used a stoma. Sixteen had mild and two had moderate LUTS. Fifteen patients completed the SSES-E, scoring an average of 80, similar to the healthy cohort (83). Renal failure or catheterization did not significantly affect the overall score. In the ICIQ MLUTSsex, patients reported no significant impact of LUTS on sexuality. However, those with moderate LUTS had lower self-efficacy than those with mild symptoms (mean 75 vs. 84). Conclusions: Although quality of life and sexual function do not appear to be significantly impaired, LUTS are common and appear to be associated with a decreased SSE in our cohort. This should be particularly considered during the transition to adult care.