An adjustable lumbar support (10) adapted to be integrated into new or existing seat structures. Adjustable lumbar support (10) includes a floating plate (15) supported by a support linkage. In one embodiment, the support linkage is defined by first and second spring members (25) and (26) which engage the seat frame. In an alternate embodiment, the support linkage is defined by first and second spring members (25) and (26) engaged with first and second linkage members (52), respectively, and includes a rotary power mechanism (50) for applying a rotating motion to a shaft (54) threadably engaged with first and second linkage members (52). The degree of support provided by floating plate (15) is adjusted by adjusting the effective length of the support linkage. Lumbar support mechanism (10) can be mounted in a seat back alone or in conjunction with an integral trim attachment array (70). Trim attachment array (70) is adapted to replace the trim wires molded into the cushion foam of a standard seat.