We present methods to determine the age and sex of Akohekohe (Palmeria dolei), an endangered Hawaiian honeycreeper, developed on the basis of 45 museum specimens and 91 live birds captured on the island of Maui. Akohekohe retained all Juvenal primaries, some Juvenal secondaries, and some body feathers after the first prebasic molt; they attained full adult plumage after the second prebasic molt. Retention of brown Juvenal body feathers, especially on the head, distinguished most birds in the first basic plumage from adults, which have a full complement of distinctive, black lanceolate body feathers with white, gray, or orange tips. Male Akohekohe were heavier than females and had longer wing, tail, and tarsometatarsus lengths. We present a linear discriminant function to sex both adults and juveniles using lengths of their wing and tarsometatarsus.