Introduction: Drug-resistant epilepsy presents high worldwide prevalence and is dificult to control despite the wide variety of available antiepileptic drugs (AED). Modifed Atkins diet (MAD) is an additional treatment alternative. Several studies have addressed the use of ketogenic diet and MADin children with drug-resistant epilepsy, but insufficient research has been conducted into adults with the same condition. Objective: To evaluate the effectiveness and tolerability of, and adherence to the MAD in adults with drug-resistant epilepsy. Material and methods: We conducted a 6-month pre-posprospective study at a reference hospital. Patients were prescribed the MADwith limited carbohydrate intake and unlimited fat intake. We conducted clinical and electroencephalographic follow-up according to the relevant guidelines, and assessedadverse effects changesin laboratory findings, and adherence. Results: Thirty-two patients with drug-resistant epilepsy were included in the study. Patients mean age was 30 years, mean disease progression time was 22 years, and all patients had focal or multifocal epilepsy. Thirty-four percent of patients presented > 50%decreasesin overall seizure frequency (P=.001); seizure control was greater in the “rst month and subsequently declined. Thesepatients presented weight loss (RR:7.2; 95%CI: 1.3-39.5; P=.02), good to fair adherence only in the first and third months (RR: 9.4; 95%CI: 0.9-93.6; P=.04 and RR:0.4; 95%CI: 0.30-0.69; P=.02, respectively). Tolerability data showed that the MADis safe: adverse effects were minor and short-lived in most cases, with the exception of mild to moderate hyperlipidaemia in one-third of patients. The adherence rate was 50%at the end of the study. Conclusions: In adults with drug-resistant focal epilepsy, the MAD showed adequate tolerability and moderate but decreasing effectiveness and adherence, probably due to a preference for a carbohydrate-based diet.