Background: Chromosome 22q13 has shown linkage with schizophrenia (SCZ) and bipolar affective disorder (BPAD). A missense mutation in MLC1 (putative cation-channel gene on 22q13) co-segregating with periodic catatonic schizophrenia has been reported. We have investigated the relationship of MLC1 with SCZ and BPAD in Southern India. Methods: All exons and flanking intronic sequences of MLC1 were screened for novel variations. Case-control (216 BPAD, 193 SCZ, 116 control subjects) and family-based analyses (113 BPAD, 107 SCZ families) were performed to evaluate association of MLC1 with these disorders. Results: We found 33 MLC1 sequence variations, including three novel mutations: Val210Ile, Leu308Gln, and Arg328His in six BPAD cases and Val210Ile in one control individual. Minor allele of a common variation, ss16339182 (in ∼6 Kb Linkage-Disequilibrium [LD]-block) was associated with BPAD in case-control (p = .03) and family-based analyses (transmitted/nontransmitted [T/NT]-44/20; p = .003). Association was observed for rs2235349 and rs2076137 with SCZ and ss16339163 with BPAD in case-control study. Using Block 2 haplotype tagging single nucleotide polymorphisms (htSNPs), GC haplotype revealed association (p = .02) and excess transmission (p = .002) with BPAD. Conclusions: Association of MLC1 with SCZ and BPAD suggests involvement of a common pathway. Rare missense mutations and common variants associated with BPAD favors hypothesis about likely involvement of both rare and common polymorphisms in etiology of this complex disorder. © 2005 Society of Biological Psychiatry.