PM20D1 is a little studied enzyme until recently, belonging to the mammalian M20 peptidase family, which catalyzes both the synthesis and hydrolysis of N-acyl amino acids (NAAs). NAAs are bioactive lipids biosynthesized from free fatty acids and free amino acids. These molecules have been associated with many biological functions; however, most of the biochemical mechanisms have not yet been described. The best-known biochemical mechanism is the one involved in thermogenesis, which also has implications for reactive oxygen species levels and cell preservation. In the last few years, genetic variation in PM20D1, as well as changes in its methylation and expression levels, have been reported to be associated with several disease phenotypes, including Alzheimer’s disease. In this review, we explore the current knowledge regarding the PM20D1 gene, including aspects such as its biology, potential functions, regulation of its expression, and role in different phenotypes such as Alzheimer’s disease, obesity, Parkinson’s disease, and several other disorders.