The few studies on deep-sea fungi in recent years (using either culturing or molecular signatures) have provided evidence on their occurrence. A majority of culture-dependent and culture-independent fungi recovered have homology to terrestrial species, indicating possible arrival in deep-sea either via wind or terrestrial runoffs. However, the presence of novel fungal sequences with less than 97% similarity to previously identified fungal sequences in public databases has also been reported. Several filamentous fungi and yeasts recovered from deep-sea sediments of the Central Indian Basin from approx. 5000 m grew under hydrostatic pressures of 20-40 MPa and 5 degrees C. Some of these fungi had unusual morphology during initial culturing and also when grown at 20 MPa/5 degrees C. Direct detection of fungal hyphae in deep-sea sediments is a daunting task as they are present in low abundance. We demonstrated the occurrence of fungal hyphae in deep-sea sediments by direct staining of the sediments with Calcofluor White, a fluorescent optical brightener. This review presents data on the occurrence, diversity and adaptations of fungi to various deep-sea habitats, with special emphasis on their possible ecological role under these extreme environmental conditions.