PTEN-induced putative kinase 1 (PINK1) is a causative gene for autosomal recessive early onset parkinsonism. Mutations in PINK1 were identified originally in PARK6-linked parkinsonism families from Italy and Spain. PINK1 contains 8 exons spanning 1.8 kb, and encodes a protein of 581 amino acids with a mitochondrial targeting motif and a serine-threonine protein kinase domain. Until now PINK1-mutation positive parkinsonism is the second frequent one next to parkin among autosomal recessive parkinsonism. Most of reported mutations were distributed throughout the serine-threonine protein kinase domain. Thus, loss of function of kinase activity of PINK1 is the most probable disease mechanism. The clinical phenotype of PINK1 -mutation positive parkinsonism is similar to that of parkin mutation positive parkinsonism. Single heterozygous mutations of PINK1 have been also identified sporadic Parkinson's disease (PD) patients. The presence of dopamine hypometabolism in asymptomatic mutation carriers suggests that single heterozygous mutations of PINK1 are risk factors for developing parkinsonism. In addition, some functional data have been shown that PINK1 protein may function as neuroprotective roles for mitochondria. Recent biochemical and morphological studies using drosophila melanogaster suggested that Parkin and PINK1 share a common pathway to maintain mitochondrial function and that PINK1 functions upstream of Parkin. Moreover, co-expression of double mutations of PINK1 and DJ-1 in cultured cells from one family with heterozygous mutations, enhanced susceptibility to MPP+ (1-methyl-4-phenylpyridinium ion)-induced cell death. These data suggest that PINK1, parkin, and/or DJ-1 could play an important role to maintain mitochondrial functions. In the other word, the mitochondrion is a good target for elucidating the pathogenesis of not only sporadic form but also monogenic form of PD.