Reflectance confocal microscopy (RCM) allows real-time, noninvasive microscopic view of the skin at nearly histologic resolution serially over time. RCM increases the sensibility and sensitivity of the diagnosis of skin tumours. RCM evaluates descriptive features of psoriasis, lupus erythematosus, contact dermatitis, and others. Three groups of optical histology have been described: psoriasiform, spongiotic, and interface dermatitis. In a multicenter study, RCM patterns of spongiotic, hyperkeratotic, and interface dermatitis have been analyzed and an algorithmic method of analysis for fast application in the clinical setting based on a multivariate analysis has been proposed. A tree decision diagram has been also established.