BACKGROUND: Bullous pemphigoid (BP) has been linked to neurological and psychiatric disorders, but no nationwide population-based study has comprehensively examined the association of various comorbidities in BP patients in Sweden. OBJECTIVES: To investigate the associations between BP and various comorbidities, comparing these conditions before and after BP diagnosis with a matched control group. METHODS: A nationwide cohort study was conducted in Sweden from 2005 to 2016, including 5,738 BP cases and 17,167 age, sex and county of residence matched controls. Multivariable Cox proportional hazard regression models were used to calculate hazard ratios (HR). Univariable logistic regression assessed pre-diagnosis comorbidities, generating prevalence odds ratios (POR) with 95% confidence intervals (CI). RESULTS: BP was associated with a significantly higher overall HR for comorbidity (HR: 2.20, 95% CI: 2.08-2.33). Before BP diagnosis, the overall comorbidity was significantly increased POR 2.72 (95% CI: 2.56-2.90). Pre-diagnosis association included dementia, Parkinson's disease, epilepsy, amyotrophic lateral sclerosis, multiple sclerosis, schizophrenia, unipolar/bipolar disorders, suicide, diabetes, stroke, systemic lupus erythematosus, systemic sclerosis, psoriasis, lichen planus, alopecia areata, and vitiligo. After diagnosis, the overall hazard ratio (HR) for comorbidities was highest within the first year (HR 2.88, 95% CI: 2.68-3.10) and remained elevated beyond one year (HR 1.57, 95% CI: 1.44-1.71). Post-diagnosis associations remained elevated for dementia, Parkinson's disease, epilepsy, schizophrenia, unipolar/bipolar, diabetes, psoriasis, lichen planus and autoimmune diseases such as systemic sclerosis and Sjögren's syndrome. CONCLUSION: BP is strongly associated with neurodegenerative, psychiatric, autoimmune, and metabolic comorbidities before and after diagnosis, highlighting their clinical significance as predisposing and prognostic factors in BP patients.