X-ray analysis of crystals of (+)-mianserin hydrobromide (1,2,3,4,10,14b-hexahydro-2-methyl-dibenzol[c,f]pyrazino[1,2-a]azepine) has established the stereochemistry and absolute configuration of this compound (S at 14b). The crystals are orthorhombic with unit-cell dimensions: a = 1299(1)pm, b = 1420(1)pm, c = 1002(1)pm; Z = 4. The space group is P212121. Intensity data for about 1000 reflections were measured on a single-crystal diflractometer with Cu-Kα radiation. The crystal structure was solved by the heavy-atom method and refined by least-squares procedures. Final R-factor 9·4%. The absolute configuration was determined by Bijvoet's technique.