Breeding of fancy mice has been a tradition in Japan. Recent progress in animal science has shed a new light on Japanese wild-derived mice as tools for discovery of new disease models because these mice, Mus musculus molossinus, are genetically far remote from the majority of available laboratory mice. After decades of effort, five inbred strains of mice have been established from pairs of wild mice trapped in Tohoku, northeastern Japan, namely KOR1/Stm, KOR5/Stm, KOR7/Stm, AIZ/Stm, and MAE/Stm. They carried numerous mutations, leading to a variety of diseases. During the inbreeding of KOR1, the first spontaneous mutation was found in the Apoe (apolipoprotein E) gene, and the mutant was later designated as spontaneous hyperlipidemic (SHL). Thereafter, a number of other mutations were discovered among wild-derived inbred strains, including atopic dermatitis, microphthalmia, dominant white spots, sebaceous gland abnormalities, and audible song-like vocalization. Furthermore, to examine the possible effects of the genetic background for these mutant genes, sets of congenic strains were generated, in which the mutant gene was introduced into at least 3 different strains of laboratory mice, including BALB/c and C57BL/6. These congenic strains have now been established as novel disease models. These wild-derived inbred strains serve as a treasure trove for novel disease models. Most of them have been deposited in the Riken BioResource Center (BRC), and some are also available from commercial breeders.