ObjectiveThe objective of this study was to examine the incidence and accumulated burden of psychiatric disorders in juvenile idiopathic arthritis (JIA) relative to the general population (GP) and to their same‐sex siblings.MethodsWe performed an observational register‐based study from July 1, 2006, to December 31, 2020, with three different study population contrasts: 1) patients with incident JIA versus five age‐ and sex‐matched GP individuals (cohort), 2) patients with incident JIA versus full same‐sex siblings (cohort), and 3) patients with prevalent JIA at age 18 versus matched GP individuals (cross‐sectional). We investigated six groups of psychiatric disorders defined via International Classification of Diseases, Tenth Revision codes: mood and anxiety, suicidal behavior, eating, sleeping, substance use, psychotic, plus an overall combined outcome (ie, at least one of the six). Incidences rates were compared through Cox regression (contrasts 1 and 2) and logistic regression (contrast 3), all adjusted for demographics, comorbidities, and proxies for socioeconomic status.ResultsDuring 25,141 person‐years of follow‐up of 4939 incident patients with JIA, the incidence of the overall combined outcome was 20.1 per 1000 person‐years in patients with JIA versus 13.1 per 1000 person‐years in the GP (adjusted hazard ratio [HR] = 1.49 [95% confidence interval: 1.35‐1.65]). The three most elevated HRs were obtained for sleeping disorder (1.91 [1.41‐2.59]), suicidal behavior (1.60 [1.23‐2.07]), and mood and anxiety disorders (1.46 [1.30‐1.64]). The comparison of patients with JIA (n = 1815) with their siblings (n = 2050) for the overall combined outcome resulted in a nonstatistically significant HR (1.16 [0.82‐1.64]). By age 18, patients with JIA were more likely to have been diagnosed with any psychiatric disorder (adjusted odds ratio = 1.37 [1.25‐1.50]).ConclusionThere is an increased burden of psychiatric morbidity in JIA, which holds both individual and familial components.