Opportunistic molds have emerged during the past decade as important causes of morbidity and mortality in some group of patients. At present Aspergillus spp. is one the most common cause of infection in bone marrow/stem cell transplant recipients and mucorales are increasingly reported as causing lethal infections, despite aggressive medical and surgical interventions. In addition, rare emerging molds are becoming a more common cause a deep and invasive fungal infections. Both hyaline hyphomycetes and black fungus species are increasingly reported as causing nosocomial mycoses (pneumonia, CNS infections and disseminated infections) refractory to conventional therapy. Fusarium spp. has been implicated in nosocomial outbreaks of respiratory and disseminated mycosis. Scedosporium spp. cause disseminated and localized infections in hospitalized patients. Paecilomyces lilacinus and Scopulariopsis brevicaulis are rare emerging hyphomycete that can cause nosocomial invasive infections in immunocompromised patients, and Alternaria spp. has been described in cases of deep infection in solid organ transplant recipients. Several factors have been signalled as causes of the emergence of rare moulds at hospital. Environmental changes, antimicrobial pressure, an expanding population of immunocompromised hosts and an increasing of capabilities to identify rare fungi are the most commonly argued. It should be noted that emergent fungal infections would continue to increase in these settings. Efforts should be made to identify nosocomial emerging molds at species level and to know susceptibility profile of these organisms. Correct characterization of these species can be significant at therapeutic level in view of their distinct antifungal susceptibility profile. DNA amplification-base methods could be used for characterization of emerging pathogens. Early diagnosis procedures and new therapeutic approaches can be also needed.