In many developing countries, people with epilepsy do not receive appropriate treatment for their condition, a phenomenon called the treatment gap (TG). We carried out a systematic review to investigate the magnitude, causes, and intervention strategies to improve outcomes in developing countries. We systematically searched MEDLINE, EMBASE, and PsycINFO databases, supplemented by a hand search of references in the key papers. The degree of heterogeneity and a pooled TG estimate were determined using metaanalysis techniques. The estimates were further stratified by continent and location of study (urban, rural). Twenty-seven studies met the inclusion criteria: twelve from Africa, nine from Asia and six from Latin America. We observed a high degree of heterogeneity and inconsistency between studies. The overall estimate of the TG was 56/100 [95% confidence interval (CI) 31.1-100.0]. The variation in estimates could possibly be explained by nonuniform TG estimation methods and the diverse study populations, among other factors. The TG was mainly attributed to inadequate skilled manpower, cost of treatment, cultural beliefs, and unavailability of antiepileptic drugs (AEDs). These factors have been addressed using different intervention strategies, such as education and supply of AEDs. Future research should estimate the TG coherently and develop sustainable interventions that will address the causes.