Introduction: Acute Encephalitis is associated with a high risk of acute symptomatic seizures, status epilepticus, and remote symptomatic epilepsy. Ketogenic diet therapies (KDT) have been established as a feasible and safe adjunctive management of refractory- and super-refractory status epilepticus. However, the role of KDT in the chronic management of Post-encephalitic epilepsy (PE) and autoimmune-associated epilepsy (AE) is unknown. This study aims to investigate the use of KDT in patients with PE and AE. Methods: A retrospective single-center case series examining adult patients with PE and AE treated with the modified Atkins diet (MAD), a KDT commonly used by adults with drug-resistant epilepsy. Results: Ten patients with PE and AE who were treated with adjunctive MAD were included. Four patients had either confirmed or presumed viral encephalitis, five patients had seronegative AE, and one patient had GAD65 AE. The median latency between starting MAD and onset of encephalitis was 6 years (IQR: 1-10). The median duration of MAD was 10 months (IQR: 3.75-36). Three patients (30%) became seizure-free, one patient (10%) achieved 90% seizure freedom, and three patients (30%) achieved a 50-75% reduction in their baseline seizure frequency, while three patients (30%) had no significant benefit. Overall, seven patients (70%) achieved ≥50% seizure reduction. Conclusion: In addition to its established role in the treatment of RSE, KDT may be a safe and feasible option for the treatment of chronic PE and AE, particularly in those with prior history of SE. Prospective studies are warranted to explore the efficacy of KDT in management of patients with PE and AE.