Remission while on anti-epileptic drug (AED) therapy and remission off AED are the only prognostic criteria defined by the International League against Epilepsy (ILAE), defining remission as 5 seizure-free years. Prognosis studies in epilepsy have investigated other prognostic categories using different designs and definitions. This systematic review explores factors that explain discrepancies in the proportion of patients reported with commonly studied prognostic categories in general epilepsy cohorts. Thirty publications (reporting 37 studies) were included. The outcome categories were classified as immediate remission (5 studies), remission off medication (7 studies), remission on or off medication (15 studies), intractability (9 studies) and no remission after relapse (1 study). The findings show the importance of qualifying estimates specifically by how they were defined in each study, study design, setting and patient population as these have implications for patient management and counselling. The ILAE should define the outcome measures and terminology to which researchers should be required to adhere in subsequent updates of their guidelines on research related to remission and intractability.