Background and objectives:Non-melanoma skin cancers (NMSCs) and psoriasis represent common hyperproliferative skin disorders. Basal cell carcinoma (BCC), and Squamous cell carcinoma (SCC),being the two most common NMSCs, can result from dysregulation of the homeostasis of keratinocyte proliferation and differentiation. Similar to the keratinocyte-derived carcinomas, psoriasis is a common disabling hyperproliferative skin disorder in which keratinocytes proliferate excessively and fail to differentiate . This work aimed at studying cases presenting with BCC, SCC and psoriasis histopathologically and immunohistochemically using AQP3 and Ki-67 . The expression of AQP3 is to be detected and compared to the expression of Ki-67, being very well established proliferation marker. This is to assess the possibility of using aquaporin 3(AQP3) as a marker of hyperproliferation.Patients and methods:Forty five patients with BCC, SCC and psoriasis, and 15 healthy participants were included. Each was subjected to short medical history and cutaneous examination. Accordingly, a provisional clinical diagnosis was reached. A skin biopsy from each case and healthy control was examined and immunohistochemistry was done for all participants using anti AQP3 and anti Ki67 antibodies, in order to assess the degree and pattern of expression of their immunohistochemical profile .Results: AQP3 expression was mainly membranous in all groups and few cases showed cytoplasmic pattern as well. It was significantly higher in the disease group (Mean: BCC=36.81±5.592, SCC=36.79±4.903, Psoriais= 37.50±6.06) more than the control (Mean=13.49±3.785) (P value= <0.01)The areas showing strong positivity for KI67 were also positive for AQP3 and they were positively correlated . On comparing Ki-67 and AQP3 between the different groups, both were significantly the highest in the psoriaisis group ( P value= 0.001 and < 0.01 respectively).Conclusion:We concluded that AQP3 can possibly serve as a proliferation marker and could be added to the list of diagnostic and prognostic tools for hyperproliferative disorders.Yet, due to the great controversy between the results of different studies concerning AQP3 , more studies should be conducted investigating the role of this new marker and verifying its mechanism of action in different proliferative disorders .