In this study Lilium regale (Liliaceae) is cited for the first time for Misiones, Argentina, where it occurs as a naturalized species, and new records for southern Brazil are added. The species description, synonymy, iconography, distribution, phenology, pollination, dispersal, vernacular names, uses, reference materials, and comments about its naturalization are included. A key to differentiate L. regale from L. longiflorum, the other naturalized Liliaceae in Argentina, is also presented.En este estudio se cita por primera vez a Lilium regale (Liliaceae) como especie naturalizada en Misiones, Argentina, y se suman nuevos registros para el sur de Brasil. Seincluye: descripción de la especie, sinonimia, iconografía, distribución, fenología, ...