System for staging melanoma based on depth of skin penetration, taken from top of granular level to deepest penetration or from base in ulcerated lesions; considered more reliable in predicting biological behavior than Clarke level. Ocular micrometer is used to obtain accurate values. Level 1, ? 0.75 mm; level 2, 0.76Ð1.5 mm; level 3, 1.51Ð3.0 mm; level 4, > 3.0 mm.