Previous studies have reported conflicting evidence concerning the contribution of declarative memory to advantageous decision-making on the Iowa Gambling Task (IGT). One study, in which the measurement of psychophysiology during the task necessitated a 10-s delay between card selections, found that six participants with amnesia due to hippocampal damage failed to develop a preference for advantageous decks over disadvantageous decks [Gutbrod, K., Krouzel, C., Hofer, H., Muri, R., Perrig, W., & Ptak, R. (2006). Decision-making in amnesia: Do advantageous decisions require conscious knowledge of previous behavioural choices? Neuropsychologia, 44(8), 1315–1324]. However, a single-case study (where psychophysiology was not measured and no delay between card selections occurred) showed that an amnesic patient developed normal preference for advantageous decks [Turnbull, O. H., & Evans, C. E. (2006). Preserved complex emotion-based learning in amnesia. Neuropsychologia, 44(2), 300–306]. We sought to resolve these discrepant findings by examining IGT performances in five patients with profound amnesia (WMS-III General Memory Index M = 63) and bilateral hippocampal damage caused by anoxia (n = 4) or herpes simplex encephalitis (n = 1). In one administration of the IGT, psychophysiology measurements were utilized and a 6-s delay was interposed between card selections. In a second administration, no delay between card selections was interposed. While age-, sex-, and education-matched healthy comparison participants showed significant learning with a gradual preference for advantageous decks in both conditions, amnesic patients, irrespective of IGT administration condition and extent of medial temporal lobe damage, failed to develop this preference. These findings strongly discount the possibility that the delay between card selections explains why amnesic participants fail to learn in the IGT, and suggest instead a significant role for medial temporal lobe declarative memory systems in the type of complex decision-making tapped by the IGT.