Aggressive prostate cancer is characterized by altered lipid metabolism and metabolic stress. At a subcellular level these changes are localized to the endoplasmic reticulum (ER) and mitochondria. Traditionally the function of these organelles has been studied separately. A growing body of evidence shows that the interaction between mitochondria and ER at specialized membrane contact sites play a key role in regulating fundamental cellular processes such as lipid synthesis, mitochondrial metabolism, calcium signaling, apoptosis and oxidative stress. In this study we have undertaken the first high resolution imaging study of prostate tissue to evaluate changes in mitochondrial ER-associated membranes (MAMs). We have analyzed the number and size of MAMs in human patient samples with varying Gleason grade groups using transmission electron microscopy. Quantification of the number of mitochondria in close spatial proximity (0–25 nm) to the ER in intermediate grade cancer compared to normal tissue, showed a prominent increase in tight membrane contacts. In control cells 15% of mitochondria associated closely with the ER compared to 75% in the transformed cells. Furthermore, the size of the contact sites in transformed cells was larger compared to control and covered 15% of the mitochondria perimeter, suggesting a more efficient lipid and calcium transfer at these contact sites in transformed prostate epithelial cells. Based on these findings we believe that organelle proximity and contact sites represent pathological features of prostate cancer, which may correlate with metabolic reprogramming occurring during prostate cancer progression. Our current efforts focus on identifying the protein complexes that mediate the associations between organelles and evaluating whether the occurrence of MAMs impacts on treatment responses and the development of treatment resistance.