Hyperthermia is a therapeutic technique used to enhance the efficacy of radiotherapy and chemotherapy in the treatment of oncological pathologies, by way of a temperature increase of 41–43°C in the target region. To validate hyperthermia devices, as well as the numerical codes used to simulate hyperthermia treatments, simple phantoms are used. This article considers the influence of phantoms’ geometry, dimensions, and considered organs, on the electromagnetic power absorption. Aim of the study was to evaluate the representativeness of such simple phantoms in terms of the power absorbed by the organs target of deep hyperthermia treatments (i.e., uterus and bladder). In particular, attention was posed on the influence of the visceral fat on the distribution of the absorbed power among the different organs. Results show that geometry and dimension does not influence the distribution of the absorbed power among the different tissues/organs (the maximum difference is 4% in the bladder). However, neglecting the presence of visceral fat greatly changes the electromagnetic power absorbed by the target organs, leading to a 23% increase of the percentage power absorbed in the uterus with respect to the complete model. This percent value corresponded to an increase in the volume‐averaged SAR of 140%.