Aspergillus terreus has a worldwide distribution in soil, constitutes the third most important cause of invasive aspergillosis in humans and is classically regarded as a strictly asexual species. Strains of A. terreus were characterized by ITS, β-tubulin and calmodulin sequences. Mating type was identified by amplifying and sequencing MAT1-1 and MAT1-2 genes. One MAT1-2 strain produced hyphal masses when crossed with four MAT1-1 strains on mixed cereal agar after 3 wk at 37 C. Cleistothecia formed inside the hyphal masses and produced asci containing smooth-walled ascospores with an equatorial protuberance. This is the first report of sexual reproduction in A. terreus.