Diabetes is a metabolic alteration characterized by a higher than normal blood glucose level. For the experimental study of the metabolic changes that occur during this illness, various animal models have been introduced: alloxan- and streptozotocin-injected animals, as well as depancreatized animals, as models for type 1 diabetes, and high-fat fed diabetic animals and laboratory animals with genetic diabetes as models for type 2 diabetes. All these models have been used to investigate specific events on the cellular and organ levels that occur as a consequence of diabetes. In particular, mitochondrial energy metabolism has been extensively studied using these experimental models for diabetes. The experimental results for the bioenergetics of isolated mitochondria harvested from different animal models for diabetes, with the exception of those obtained with high-fat fed diabetic animals, are conflicting; nevertheless, many researchers now consider mitochondrial energy dysfunction as one of the direct causes of the serious complications, in various organs and tissues, that are exhibited as a result of this illness. For this reason, it is important that future research clarify the true energy functional state of these organelles isolated from diabetic animals. In the present paper, the published data on this controversial but important issue of the energetic functioning of the mitochondria isolated from diabetic animals is reviewed. This paper also includes commentary on the status of current research and makes useful suggestions for the future direction of research on this topic. Keywords: Alloxan, diabetes, genetic diabetes, Goto-Kakizaki rats, mitochondrial respiration, pancreatectomy, streptozotocin.