The ontogeny of the fruit bodies of Mycena stylobates was studied by light microscopy and scanning electron microscopy (SEM). The ontogeny was divided into two phases: first the primordium with all the structures of the mature fruit body was established, then the primordial stipe elongated rapidly and the exposed hymenium started producing spores immediately. The first detected stage of fruit body formation was an irregularly arranged hyphal structure within the substrate colonized. After the rupture of the surface of the substrate, the primordium established on the surface. Soon a layer of wrapping hyphae was differentiated, which covered the complete primordium. The structures of the stipe and the cap developed synchronously. The developing stipe, cap and basal disc together formed a secondary ring-like cavity, in which the development of the hymenophore took place. The lower side of the cap was covered by a layer of degenerated hyphae. The development of the hymenophore started with a number of small alveolae on the lower side of the cap, which were covered with a hymenophoral palisade. The margins of these alveolae formed the primary lamellae, which in the first stage of their development were covered by a layer of degenerated hyphae. The hymenophoral palisade spread from the developing alveolae to the lamellar edge; the edge of the primary lamellae was forked in the early stages. Secondary lamellae were formed by the down folding of ridges from the lower side of the cap. In contrast to the primary lamellae, they were covered with hymenophoral palisade from the beginning. Spore production started immediately after the elongation of the stipe. These results were compared with other known modes of ontogeny within the Agaricales and some comments on the terminology used for the description of basidiome morphogenesis are made.