An undergarment, such as a diaper, includes a hidden central core pocket for receipt of an absorbent pad. The pocket is formed between an inner, fluid permeable layer and a fluid isolation layer. The fluid isolation layer is attached to the inner or anchor layer and is located between the inner layer and an outer layer to which the inner layer is attached. The pocket is narrower than the outer to isolate fluids from edges of the outer layer and from diaper leg openings. Both the fluid isolation layer and the outer layer may be fluid resistant to provide additional protection against leakage. Adjustment fasteners on the outside of the outer shell permit size adjustment for the diaper and the adjustment fasteners are positioned within the periphery of the pocket so that presence of the absorbent pad will enhance comfort.