The intricacies and difficulties in measuring forgetting rates, both in healthy participants and in clinical patients, have been intensively investigated since the 1970s. In recent years, there has been a revival of interest in ‘long-term’ forgetting rates, particularly in transient epileptic amnesia (TEA) and temporal lobe epilepsy (TLE), and some ‘old’ lessons have had to be re-learned.

Studies of long-term forgetting in patient groups will be reviewed, together with variables that influence different patterns of forgetting. In particular, I will report findings from two recent studies of TLE, as well as other related investigations.

Studies indicate that an impairment in memory ‘acquisition’, rather than differences in ‘long-term’ forgetting, appear critical in amnesic disorders, sometimes associated with differences in ‘early’ forgetting on recall memory measures only. An exception may be the effect of seizures, whether in consequence of epilepsy or ECT, which sometimes, but not always, appears to accelerate forgetting rates. Another important finding has been the pronounced variability in forgetting rates, both between individuals within a patient group and within individuals tested on separate occasions, making inferences from single-case studies problematical.

Findings will be interpreted in the light of these observations.