BACKGROUND: Epidemiological evidence for specific long-term conditions is required to inform best practices regarding the substantial health inequalities experienced by sexual minority individuals compared with heterosexual peers. AIM: To describe inequalities in long-term conditions among sexual minority (lesbian, gay, and bisexual [LGB]) adults. DESIGN & SETTING: Cross-sectional analysis of 1 341 339 nationally representative survey responses from the English GP Patient Survey (GPPS). METHOD: Stratifying by sex, the weighted prevalence and covariate-adjusted association of 15 long-term conditions were calculated, comparing sexual minority and heterosexual adults, considering variation by sexual orientation and variation in sexual orientation inequalities by deprivation, ethnic group, region, and age. RESULTS: After adjusting for deprivation, ethnic group, region, and age, 13 long-term conditions (all except cancer and hypertension) were more prevalent among sexual minority women than their heterosexual peers, with the largest inequalities for mental health problems (odds ratio [OR] 2.8, 95% confidence interval [CI] = 2.7 to 3.0), neurological conditions (OR 1.7, 95% CI = 1.5 to 1.8), dementia (OR 1.6, 95% CI = 1.3 to 1.9), and back problems (OR 1.4, 95% CI = 1.3 to 1.5). It was found that nine long-term conditions were also more prevalent among sexual minority men including mental health problems (OR 2.3, 95% CI = 2.2 to 2.4), 'all other conditions' (OR 1.8, 95% CI = 1.7 to 1.8), neurological conditions (OR 1.5, 95% CI = 1.4 to 1.6), and kidney or liver disease (OR 1.4, 95% CI = 1.3 to 1.5); inequalities were often largest for bisexual adults. Inequalities did not vary significantly by deprivation, ethnic group, or region except for mental health problems. Inequalities in multimorbidity were highest at younger ages; for example, LGB women aged 18-24 years had multimorbidity at the same level (approximately 20%) as heterosexual women aged 45-54 years. CONCLUSION: Sexual minority adults, especially bisexual adults, are at elevated risk for many long-term conditions and multimorbidity; this risk spans socioeconomic status and ethnic group, representing a significant healthcare challenge.