The pupa of Chaoborus albatus has never been described, although Cook (1956) presented descriptions and keys to the immature stages of most Nearctic Chaoborus species, including the larva of C. albatus. Particular emphasis is given below to determining those characters of the C. albatus pupa which distinguish it from the other Chaoborus species with which it is sympatric, especially its close consubgener, C. punctipennis. I have used the same anatomical features as Cook found most useful for Chaoborus pupae, and have constructed a key for the identification of the four eastern species recently cataloged by Cook (1965).