BACKGROUND: Significant associations have been described between climatic factors and human health, which can occur in dermatologic diseases too. OBJECTIVE: To determine the influence of the climatic factors on the medical attentions of dermatologic diseases in a general hospital in Lima (Peru). PATIENTS AND METHODS: Observational study which was carried out in a national hospital between January 2004 and December 2007. The diagnoses were classified according to the ICD-10 system. The climate information was provided by the National Oceanographic and Atmospheric Administration from USA (NOAA). RESULTS: 3 294 patients were included in the study, the average age was 35.4 ± 20.7 years old, and 53.2% were females. The "El Niño" phenomenon was associated with an increase in the prevalence of actinic keratosis (p=0.002), viral warts (p=0.001) and rosacea (p=0.014). The "La Niña" phenomenon was associated with a reduction in viral warts (p=0.026). Spring was associated with an increase of dermatitis (p=0.003), and summer was associated with an increase of benign neoplasms (p=0.049). CONCLUSION: The climatic variations influenced the occurrence of certain dermatologic diseases. The present study may represent an orientation guide to specialists and general practitioners identifying the most common dermatologic diagnoses and thus enabling better preparation to treat these cases in determined seasons of the year. ©2010 by Anais Brasileiros de Dermatologia.