Background: Coccidioidomycosis is caused by a soil fungus Coccidioides immitis and C. posadasii and its endemic in certain parts of Southern USA and in northern Mexico. It is commonly known as Valley Fever. During 2014, the states of Arizona and California, USA reported an incidence of 5,624 and 2,243 coccidioidomycosis human cases respectively. In Mexico, the last national epidemiological report that referred the incidence of confirmed coccidioidomycosis cases was published in 1994, with an unexpected geographical distribution: the states with the highest incidence were Chiapas (south eastern) and Tamaulipas (northeast), reporting 161 and 80 cases respectively. Previous studies have reported the presence of Coccidioides detected with anti-coccidioides antibodies from soil and rodent faeces near Hermosillo, Sonora, border with Arizona and in a rural area called Valle de las Palmas, Baja California, border with California. The aim of this study was to analyse the prevalence of positive coccidioidomycosis skin tests in humans on two Mexican populations located in Sonora and Baja California, Mexico. Methods & Materials: Four applications of intradermal reaction with coccidioidin antigen were carried out, two of them near Hermosillo and the other two in the rural area of Valle de Las Palmas, in both populations; the tests were applied in rainy season (November 2015) and dry season (May 2016). Coccidioidin was injected below the skin surface in the forearm of 247 individuals (Hermosillo) and 273 (Valle de las Palmas). The tests were measured after 48 hours of the application. Results: In Hermosillo, 152 (55.4%) tests were positive, from which, 62 (46.6%) were in rainy season, and increased to 90 (63.9%) in dry season. For Valle de Las Palmas 18 (6.6%) tests were positive: 5 (3.6%) in November and the number were increased to 13 (9.6%) in May. Conclusion: These findings indicate that the prevalence of positive coccidioidomycosis tests were higher in the population of Hermosillo as apposed to Valle de Las Palmas and suggest a higher incidence of this mycosis, evidencing underreporting of the infection. Also, this study shows that climatic factors have an influence in the prevalence of positive tests in these regions.