A Nordic External Quality Assessment programme in medical mycology was established in 2005. In order to monitor not 'best practice' but the level of routine diagnostics, specimens were designed to resemble clinical samples and laboratories were asked to handle the samples like routine samples. Five simulated clinical samples were distributed to 59 participating Nordic laboratories of clinical microbiology. The specimens contained the following microorganisms: 1) Candida glabrata and C. albicans in a ratio of 1:20; 2) Cryptococcus neoformans; 3) Aspergillus fumigatus, C. albicans and Enterobacter cloacae; 4) C. tropicalis, Klebsiella pneumonia and Enterococcus faecium; 5) None. 66% of the laboratories failed to detect the C. glabrata isolate in sample no. 1. 34% of the laboratories reporting susceptibility results incorrectly reported the Cryptococcus neoformans isolate as fluconazole susceptible. 24% of the laboratories failed to detect Aspergillus fumigatus in specimen no. 3 despite the accompanying clinical information notifying that it was a BAL sample from a neutropenic patient in an ICU. In conclusion, this distribution of simulated clinical samples illustrates that the traditional quality assessment programmes may give a false sense of satisfactory performance, that mycological diagnosis is difficult, and that there is a need of further improvement and attention.