A releasably locking dilator and sheath assembly (10, 200, 300) and methods for releasing the dilator (12) from and longitudinally splitting the sheath (14). The assembly includes a dilator having a dilator hub (20) and a sheath having a sheath hub (40, 240). The sheath hub has a valve (260, 360) and two opposing winged tabs (42), each tab having a perpendicular portion (44) and an angled portion (46), as well as having a female locking portion (53). The dilator hub has a male locking portion (30) designed to engage the female locking portion of the sheath hub. The dilator is released from the sheath by rotating the dilator 90° in relation to the sheath and pulling the dilator out of the sheath. The sheath is longitudinally split by creating a couple on each of the winged tabs (42) thereby forcing the sheath and the sheath hub to split longitudinally.
