IntroductionThe Morisky Medication Adherence Scale (MMAS-8) is widely used to assess medication adherence, yet its psychometric properties have not been evaluated in Ecuador.ObjectiveThis study examined the reliability, factorial structure, and convergent validity of the MMAS-8 in Ecuadorian patients diagnosed with neuropsychiatric disorders.ResultsA total of 440 patients with neuropsychiatric disorders completed the MMAS-8. Internal consistency was evaluated with Cronbach’s alpha and McDonald’s omega. Confirmatory factor analysis (CFA) supported the original one-factor model with adequate fit (RMSEA = 0.08, SRMR = 0.06, CFI = 0.92, TLI = 0.90, α = 0.70, ω = 0.71). A two-factor model was also examined. Confirmatory factor analysis (CFA) supported the two-factor model with adequate fit (RMSEA = 0.08, SRMR = 0.07, CFI = 0.92, TLI = 0.90, α = 0.70, ω = 0.72). The scale showed acceptable internal consistency (ω = 0.71), and all items correlated positively (r > 0.20; p < 0.001). A two-factor solution produced only a slight improvement in model fit.ConclusionThe MMAS-8 appears to be a reliable and valid instrument for assessing medication adherence in Ecuadorian patients with neuropsychiatric disorders, supporting its use in clinical practice and research.