Even if being a neoplastic disease, mycosis fungoides is listed in this article as a major differential diagnosis from several inflammatory skin disorders. In particular, differentiation between chronic dermatitis and early stage mycosis fungoides is often highly problematic. In dermoscopical studies, significant differences have been shown: In contrast to the dotted vessels in dermatitis, mycosis fungoides reveal short linear vessels and orange-yellowish areas. In addition, in mycosis fungoides a peculiar vascular structure is frequently observed consisting of a dotted and a linear component (spermatozoon-like structure). In the assessment of a chronic lesion previously diagnosed as dermatitis, dermoscopic examination is expected to reveal dotted vessels, occasionally combined with yellowish scales. Lesions under long-term treatment with topical steroids represent the only exception to this rule. When, instead, dermoscopy reveals linear vessels, the suspicion of mycosis fungoides rises strongly and in this case, patient’s management should be adjusted accordingly.