There are approximately 70000 species of described fungi, representing about 5% of the estimated 1·5 M species world-wide. Proportionally there are numerous undescribed species and most habitats and hosts should provide a bounty of novel fungi that can be exploited in a wide variety of ways. Where, however, are these missing fungi? Data indicates that they may occur in poorly studied countries, hosts, habitats, niches or tissues, and are mostly microfungi. Host specificity and/or tissue recurrence are important considerations in biodiversity estimates. We are a long way from establishing where we can find the missing 1·43 M fungi, but evidence presented here resulting from data from Hong Kong indicates many places where we could look.