A region between D13S71 and D13S274 on 13q32 showed linkage to bipolar disorder (BP) based on a genome scan using markers with an average spacing of ∼6 cM and an average heterozygosity of ∼60% [Detera-Wadleigh et al., 1999: Proc Natl Acad Sci USA 96:5604–5609]. In an attempt to confirm this finding and achieve fine mapping of the susceptibility region, nine additional microsatellite markers with average heterozygosity of ∼86%, located between D13S71 and D13S274, were typed in the same sample. The strongest linkage evidence was detected by multipoint linkage analysis (ASPEX program) around D13S779–D13S225 with maximum LOD score of 3.25 under Affection Status Model II (ASM II; P = 0.0000546). Data from additional nine markers resulted in a decrease of the 95% confidence interval of the linkage region. Association analyses with GASSOC TDT and ASPEX/sib_tdt detect potential linkage disequilibrium with several markers, including D13S280 (ASPEX TDT P = 0.0033, ASM I). These data generated using a higher marker density within the proposed susceptibility region strengthen the validity of our previous findings and suggest a finer localization of the susceptibility gene(s) on 13q32. © 2001 Wiley-Liss, Inc.