A knit sock includes a foot portion having an upper instep area and a lower sole area integrally knit of a body yarn in circumferential courses and axial wales. The lower sole area defines inner and outer arch regions. The inner arch region incorporates a targeted compression zone adapted to reside generally adjacent an inner arch of a wearer's foot. The compression zone includes axially extending compression ridges of variable length spaced apart from a top of the compression zone to a bottom of the compression zone. When the sock is worn, a compression force applied by the foot portion within the targeted compression zone is greater than the compression force in directly adjacent areas of said foot portion.