In humans, it is not possible to obtain experimental evidence of when a cancer begins to metastasize. The purpose of this study was to estimate the time of onset of metastatic dissemination in cutaneous melanoma using a model based on its growth rate (GR). The critical time of onset of metastatic dissemination below which no cases of fatal melanomas were seen may be described with a potential function in which this time is inversely proportional to the GR. The critical time of development beyond which a melanoma may metastasize presents great variation. This time was just 1 month for those melanomas with a fast GR, whereas it was over 5 years for those with a very slow GR. Quantitatively, the fastest-growing melanomas began metastasizing with a greater thickness than the slowest-growing melanomas. A correlation exists between the critical time of onset of metastatic potential and the GR of the melanoma. These results may well have relevance to the understanding of mechanisms of tumor dissemination and for the design of future studies on melanomas, irrespective of whether they are basic studies on biomolecular mechamisms or clinical studies.