BackgroundPatient multimorbidity and GP burnout are increasing problems in primary care and are potentially related.AimTo examine whether patient multimorbidity was associated with GP burnout in a Danish primary care setting.Design and settingQuestionnaire data from 1676 Danish GPs and register data on their patients.MethodGPs completed the Maslach Burnout Inventory. Patients listed in a national registry with ≥2 chronic physical diseases from a list of 10 were classified with multimorbidity. For each practice, crude and sex- and age-standardised rates of multimorbidity were calculated, the latter computed as a weighted average with the weights taken from a reference population (5 646 976 Danish citizens). Data were analysed with logistic regression and adjusted analyses included GPs’ age and sex, number of GPs in practice, and socioeconomic deprivation among patients as covariates.ResultsA high crude rate of patient multimorbidity increased GPs’ likelihood of burnout (odds ratio [OR] 1.79, 95% confidence interval [CI] = 1.13 to 2.82), and when adjusting for covariates the association remained significant when comparing GPs in the third highest quartile of the multimorbidity rate against GPs in the lowest quartile (OR 1.64, 95% CI = 1.02 to 2.64). The sex- and age-standardised patient multimorbidity rate was not associated with GPs’ likelihood of burnout.ConclusionA high crude rate of patient physical multimorbidity increased the likelihood of burnout among GPs. The sex- and age-standardised rate of multimorbidity was not related to GPs’ likelihood of burnout. Thus, the absolute amount of multimorbidity, and not the relative, affects the GP’s burnout risk. GPs with high numbers of patients with complex needs should be supported to prevent suboptimal care and GP burnout.