Circadian rhythm is a fundamental physiological feature of essentially all living organisms, including simple cell structures as well as complex organisms. Numerous behavioral and physiological processes in the orgranism underlie rhytmical changes. Circadian rhythm refers to biological rhythm that is synchronized with day-night changes in environment and lasts approximately twenty-four hours. These daily day and night changes directly affect physiological and morphological functions in individual organisms and are refered as external signals such as light and food. On the molecular level, circadian rhythm is governed by so-called core clock genes which control a wide range of circadian rhythms in physiological processes and behavior. Deregulation of these rhythms in mammals is associated with different pathological conditions including carcinogenesis. Due to changes in everyday lifestyle in last years, there have been increased number of malignant melanoma cases. Melanoma is malignant tumor which appears in existing naevus or even on healthy skin. It starts as malignant transformation of pigment cells, melanocytes, and it is assumed that the exposure to intense ultraviolet radiation, along with family anamnesis, still remains the main reason for tumor development. It is considered that deregulation of circadian rhythm or its resynchronization plays a big role in the progression of the disease. The aim of this thesis is to elaborate the topic of the influence and correlation of the circadian rhythm perturbation and clock gene involvement in melanoma pathogenesis. Growing body of evidence points out that clock genes are involved in tumor development and the regulation of of their expression might be used as potential therapy in treatment of cancer patients.