Background: Physicians' work conditions and mental well-being may affect healthcare quality and efficacy. Yet the effects on objective measures of healthcare performance remain understudied. This study examined mental well-being, job satisfaction and self-rated workability in general practitioners (GPs) in relation to hospitalisations for ambulatory care sensitive conditions (ACSC-Hs), a register-based quality indicator affected by referral threshold and prevention efforts in primary care. Methods: This is an observational study combining data from national registers and a nationwide questionnaire survey among Danish GPs. To ensure precise linkage of each patient with a specific GP, partnership practices were not included. Study cases were 461 376 adult patients listed with 392 GPs. Associations between hospitalisations in the 6-month study period and selected well-being indicators were estimated at the individual patient level and adjusted for GP gender and seniority, list size, and patient factors (comorbidity, sociodemographic characteristics). Results: The median number of ACSC-Hs per 1000 listed patients was 10.2 (interquartile interval: 7.0-13.7). All well-being indicators were inversely associated with ACSC-Hs, except for perceived stress (not associated). The adjusted incidence rate ratio was 1.26 (95% CI 1.13 to 1.42) for patients listed with GPs in the least favourable category of self-rated workability, and 1.19 (95% CI 1.05 to 1.35), 1.15 (95% CI 1.04 to 1.27) and 1.14 (95% CI 1.03 to 1.27) for patients listed with GPs in the least favourable categories of burn-out, job satisfaction and general well-being (the most favourable categories used as reference). Hospitalisations for conditions not classified as ambulatory care sensitive were not equally associated. Conclusions: ACSC-H frequency increased with decreasing levels of GP mental well-being, job satisfaction and self-rated workability. These findings imply that GPs' work conditions and mental well-being may have important implications for individual patients and for healthcare expenditures.