An implantable port assembly (10) having a lower housing (12) and an upper housing (14) and at least one chamber (20,22) and a corresponding septum (16,18) associated therewith. The upper housing (14) includes a plurality of latch arms (30) depending therefrom that latch with corresponding catches (34) of the lower housing for mechanically securing the assembly together during bonding or welding. Each septum (16,18) includes a peripheral flange (40) held in compression by and between the upper and lower housings (14,12) upon and after assembly. In a dual port assembly (10), a pair of septa (16,18) are disposed side-by-side with overlapping flanges (54), and the upper housing (14) includes posts (52) extending through apertures (54) through the overlapping flanges (56) that extend into holes (58) in the lower housing (12).