Objective To study socio-demographic and clinical aspects, as well as psychiatric co-morbidity that influence the quality of life of adult epileptic patients. Methods One hundred and thirty-two individuals diagnosed with epilepsy were evaluated from neurological/clinical and psychiatric points of view and by the Quality of Life in Epilepsy Inventory (QOLIE-31). Predictive factors for the QOLIE-31 scores were studied. Results The regression analyses indicated the existence of psychiatric co-morbidity (total score, seizure worry, emotional well-being, energy/fatigue, social function and cognitive function) and a greater seizure frequency (total score, cognitive function and energy/fatigue) as predictive factors for lower scores in the total QOLIE-31 score and in various dimensions. Abnormalities in the neurological exam and poly-therapy with anti-epileptic drugs were negative factors limited to one of the dimensions cognitive function and social function, respectively. Conclusion The presence of psychiatric co-morbidity and a greater seizure frequency were the main factors influencing the quality of life in epileptic patients as evaluated by QOLIE-31.