Because of its minimally invasive nature, thermal ablation is increasingly performed in patients with renal cell carcinoma (RCC) who are poor surgical candidates. Thermal ablation has been associated with excellent outcomes, and thus has been regarded as a viable alternative to nephron-sparing surgery. Many papers report minimal to no reduction in renal function after ablation therapies. However, in order to achieve good local control, normal renal tissue must be sacrificed, subsequently leading to reduced renal function. The amount of normal renal tissue to be ablated depends on the size, location, and number of RCCs, as well as the type of thermal ablation applied. However, there are few reports about what reduces renal function following thermal ablation therapies. The purpose of this review was to discuss factors that affect reduction in renal function and to assess the relationship between local tumour control and renal function.