As part of a continuing investigation of the relationship between dietary factors and cognitive function, the present study examined the combined effects of environmental influences and high-fat diets on learning and memory. Following 3 months of dietary (20% by weight fat diets, composed primarily of either beef tallow or soybean oil versus standard laboratory chow) and environmental treatments (standard, enriched or impoverished), subjects were tested on a variable interval delayed alternation (VIDA) task which measures learning and memory functions that differentially involve specific brain regions. The results confirmed the negative effects of high fat diets, relative to chow, on all aspects of VIDA performance and showed that environmental enrichment overcame deficits associated with dietary fat. Housing rats fed high-fat diets in an impoverished environment did not further exacerbate cognitive deficits observed in such rats living under standard conditions. By comparison, chow-fed rats exhibited no benefit associated with the enriched environment on any aspect of task performance, and only a transitory learning impairment when housed in an impoverished environment. The results show that high fat diets and environmental conditions influence cognitive function and that these two factors interact with one another to produce different profiles of benefits and impairments.