We herein report the results of a retrospective nationwide survey on mycoses diagnosed between January and December, 2004. The study included data provided by 72 laboratories located in 19 provinces and in Buenos Aires City. Out of 801,805 microbiological specimens processed that year, only 62,681 (8%) were submitted to mycological studies. A total of 23,600 mycoses cases were diagnosed: 11,107 (47%) superficial mycoses, 10,830 (46%) mucosal candidiasis and 1,663 (7%) deep mycoses. Relative frequencies of superficial mycoses did not differ significantly (p > 0.05) from frequencies observed in a previous study covering Buenos Aires City and Province (1993), and from two countrywide surveys conducted by the National Network of Mycology Laboratories and National Quality Control Program (NNML and NQCP) in 1999 and 2002. The most frequent deep mycoses were yeast fungaemia (34%), cryptococcosis (20%), broncho-pulmonary aspergillosis (13%), histoplasmosis (11%), paracoccidioidomycosis (7%) and pneumocystosis (5%). In contrast with results of four previous nationwide studies on broncho-pulmonary mycoses including a survey performed by NNML and NQCP in 2002, our study revealed that histoplasmosis prevailed over paracoccidioidomycosis, thus ranking for the first time as the most frequent endemic mycosis in Argentina.