It has a total length of 45–55 cm (18–22 in), with the Australian subspecies larger than subspecies from New Guinea and nearby islands. The plumage is overall white, while the underwing and -tail are tinged yellow. The expressive crest is yellow. The bill is black, the legs are grey, and the eye-ring is whitish. Males typically have almost black eyes, whereas the females have a more red or brown eye, but this require optimum viewing conditions to be seen. The differences between the subspecies are subtle. C. g. fitzroyi is similar to the nominate race but lacks the yellow on the ear tufts and slightly blueish skin around the eye. C. g. eleonora is similar to C. g. fitzroyi but is smaller and has broader feathers in the crest, and C. g. triton is similar to C. g. eleonora except it has a smaller bill.
It is similar in appearance to the three species of corellas found in Australia. However, corellas are smaller, lack the prominent yellow crest and have pale bills. In captivity, the Sulphur-crested Cockatoo is easily confused with the smaller Yellow-crested Cockatoo or the Blue-eyed Cockatoo with a differently shaped crest and a darker blue eye-ring.