Cyclin-dependent serine-threonine kinases, among them D1 cyclin, are responsible for cell cycle regulation in the G1 phase. Cyclins, as well as proteins cooperating with them, are broadly investigated, because their dysfunction may lead to neoplastic transformation. In this article we present an overview of the literature concerning cyclin D1 expression in: gastric cancer, breast cancer, prostate adenocarcinoma, colon and rectum cancer, lung adenocarcinoma, idiopathic pulmonary fibrosis, and squamous cell carcinoma of the head and neck. The authors have underlined the articles were cyclin D1 expression is studied in: skin cancers (squamous cell carcinomas and basal cell carcinomas), dysplastic nevi and malignant melanoma.