Rembrandt van Rijn (1606-1669) left behind the largest collection of self-portraits in the history of art. These portraits were painted over a period of 41 years, using a realistic technique. To evaluate Rembrandt's aging process we studied 25 uncontested Rembrandt oil self-portraits by means of objective and descriptive techniques. By measuring brow position changes through the years, we demonstrated that brow descent started in the second half of the third decade and began to level out in the fourth decade. Based on Rembrandts' aging physiognomy, from age 22 to 63, we believe that Rembrandt did not suffer from temporal arteritis, hypothyroidism, rosacea, or rhynophima and that no other facial signs of systemic diseases are evident, contrary to the opinions expressed by other medical professionals. We suggest that Rembrandt suffered from melancholia or mild depression, and propose the possibility of chronic lead poisoning as a theoretical illness that he might have had.