In a prospective study, 50 cases of paranasal sinus mycoses were diagnosed in 2 years out of 119 clinically suspected patients from north India. Young men from rural areas were most commonly afflicted. Patients with paranasal sinus mycoses could be grouped in three clinical varieties: noninvasive, 31; invasive, 17; allergic, 2. Maxillary and ethmoid were the common sinuses concurrently involved in these patients, whereas sphenoid and frontal sinuses were also affected in invasive variety. Aspergillus flavus (80%) was the most common isolate, followed by A. fumigatus (6%). Alternaria species was identified in two patients with noninvasive granuloma. In invasive variety, Rhizopus arrhizus and Candida albicans were the causative agents in two patients and one patient, respectively. Regarding pathogenesis besides epidemiologic factors, the immunologic factors were also evaluated. It was found that presence or absence of precipitating antibody against antigens from the etiologic agents correlates well with disease progression. Allergic factor was found in all varieties, though presence of cell-mediated immunity was demonstrated in 29% patients with noninvasive granuloma only. The combination of skin test against aspergillin and precipitin demonstration at the outset will therefore help in preliminary screening.