PURPOSE: Neurobehavioral problems (i.e., cognitive impairment/behavior problems) are a major challenge in childhood epilepsy. Yet there are limited data in children with early-onset epilepsy (CWEOE; onset ≤4 years), the period in which the incidence of childhood epilepsy is highest. This study aimed to determine the prevalence, spectrum, and risk factors for neurobehavioral problems CWEOE. METHODS: This prospective, population-based, case-controlled study identified children with newly diagnosed early-onset epilepsy in South East Scotland using active multisource capture-recapture surveillance (May 2013 - June 2015). The CWEOE and controls completed an age-appropriate neurobehavioral assessment battery across seven domains: general cognitive ability (GCA), adaptive behavior, externalizing, internalizing, executive functioning, social functioning, and Autism Spectrum Disorder (ASD) risk. RESULTS: Fifty-nine CWEOE were identified with an ascertainment of 98% (95% confidence interval [CI] 94, 103). Forty-six (78% [95% CI 65.9, 86.6]) CWEOE (27 male, median age 25.5, range 1-59, months) and 37 controls (18 male, median age 31.5, range 3-59, months) consented for study entry. The CWEOE were similar to controls in gender, age, prematurity, and family history of psychopathology, but not socioeconomic status (Fisher's exact test [FET] < .001). Neurobehavioral assessments were carried out a median of 2.97 (Interquartile range [IQR] 1.51-4.95) months post epilepsy diagnosis. More CWEOE (63% [95% CI 48.6, 75.5]) had neurobehavioral problems compared with controls (27% [95% CI 15.4, 43.0]); p < 0.01. This observation was independent of socioeconomic status. Multidimensional problems were prevalent in CWEOE with 43% having two or more different domain-level problems; GCA impairment, adaptive behavior, internalizing, social functioning, and ASD risk were particularly marked. Risk factors varied by domain. DISCUSSION: This novel study using comprehensive psychometric assessments found that neurobehavioral problems in CWEOE were detectable, common, and multidimensional. The degree of cooccurrence implies that problems are the norm, and multidimensional screening should be considered at epilepsy onset. The findings could aid policy development on health and educational provision in CWEOE.