This study analyzed the occurrence of learning disability (LD) in adults with childhood-onset epilepsy and the impact of LD on medical and social outcome. Any LD occurred in 76%: in 57% of mentally normal (IQ>85), in 67% of mentally near-normal (IQ=71-85), and, self-evidently, in all mentally retarded (IQ<71) adults. Half of the patients (51%) with LD had mental retardation. In multivariate analysis, mental retardation and subsequent LD were predicted by occurrence of cerebral palsy (odds ratio [OR]=3.83; 95% confidence interval [CI]=1.77-8.28, P=0.0006), onset of epilepsy before the age of 6 years (OR=3.63, 95% CI=1.57-8.42, P=0.0026), and poor early effect of drug therapy (OR=2.78, 95% CI=1.43-5.39, P=0.0025). Among mentally normal or near-normal subjects, a symptomatic etiology of epilepsy was the only predictor (OR=7.72, 95% CI=3.02-19.76). The degree of LD significantly affected medical, social, and educational long-term outcomes.