Abstract The aim of this study is the taxonomic revision of the genus Frullania Raddi in Portugal and Madeira. The revision is based on the study of morphological variation in about 1500 specimens, recently collected or borrowed from different herbaria. The present investigation was initiated with the morphological analysis of 79 characters from 313 selected specimens; 32 quantitative and 47 qualitative characters were defined, based on vegetative and reproductive structures. The quantitative characters include the mean length and width of the following: dorsal lobe, lobule, stylus, hemiphyll, underleaf, median cells, androecia, perianths and perianth wall cells, capsules and inner wall cells, elaters and spores. The qualitative characters were binary-coded and complement the quantitative characters. Among the characters considered were the form of the lobe apex and base, the type of lobule, the extent of revoluteness along the margins of the underleaves, the length of the sinus and the underleaf base, perianth morphology and the rosette pattern along the equatorial walls of the spores. The multivariate analysis of the range of morphological variation of each Frullania species from Portugal and Madeira, and the detection of the diagnostic characters of each taxon were also performed. The description of each taxon includes details of the type and the main synonyms. Some comments concerning the variability and relation to closely allied taxa are also given, as well as notes on the ecology and distribution of each species. Frullania azorica and Frullania polysticta are restricted to the Azores, Madeira and the Canaries.