Background Little is known about the association between cataract and multimorbidity. Therefore, the aim of the present study was to examine the relationship between cataract and chronic conditions and multimorbidity in a large representative sample of Spanish adults. Methods This study used data from the Spanish National Health Survey 2017, a cross-sectional sample of 23,089 adults aged >= 15 years from Spain [54.1% female; mean (standard deviation) age 53.4 (18.9) years]. Cataract and 30 other physical and mental chronic conditions were self-reported. Multimorbidity was defined as the presence of at least two physical and/or mental chronic conditions (excluding cataract). Control variables included sex, age, marital status, education, smoking, and alcohol consumption. Multivariable logistic and negative binomial regression analyzes were conducted to assess associations. Results The prevalence of cataract and multimorbidity was 12.5% and 56.5%, respectively. All chronic conditions were significantly more frequent in individuals with than in those without cataract. Overall, there was a positive relationship between cataract and multimorbidity [odds ratio (OR) = 2.77; 95% confidence interval (CI): 2.39-3.21]. In addition, cataract was significantly associated with the number of chronic conditions in the whole population [incidence rate ratio (IRR) = 1.34; 95% CI: 1.29-1.38]. Conclusions Cataract is positively associated with chronic conditions and multimorbidity in adults. Interventions specifically designed for those with cataract to reduce or manage co-occurring chronic conditions and multimorbidity are urgently required.