Melanonychia is pigmentation of the nail plate due to melanocyte activation or proliferation. Longitudinal melanonychia is the most common pattern. There are many etiologic factors depending on the number of nails involved and the dermoscopic features of the nail. These include trauma, infection, malignancy, pregnancy, dermatologic diseases, and medications (Jefferson J, Rich P. PMID: 22792094, PMCID: PMC3390039. In: Melanonychia. https://doi.org/10.1155/2012/952186 ). One or more than one fingernails or toenails may be involved and may occur at any age. The history and clinical and dermoscopic features are instructive as to whether it is benign or malignant (Baykal C. Atlas of dermatology. 4th ed). Melanonychia may present as a longitudinal band, transverse band or total melanonychia involving the entire nail. Since melanonychia requires biopsy for definitive diagnosis and biopsy can be invasive and may lead to nail dystrophies, biopsy is not performed in all lesions. Clinical examination and dermoscopic findings help to make the correct diagnosis and reduce the number of unnecessary surgeries (Demirdağ HG, Akay BN. Melanonychia. In: Türkiye Klinikleri, pp 16–22, 2020). Melanocytes are found in the matrix and nail bed. The majority of these melanocytes are inactive. When triggered by trauma, infection, inflammation, etc., melanocytes are activated, begin to synthesize melanin and these melanin-rich melanosomes are transferred along dendrites to matrix cells. These matrix cells move distally and appear as pigmentation in the nail bed. Melanocytes also proliferate to form structures such as nevi, lentigo and malignant melanoma (Jefferson J, Rich P. PMID: 22792094, PMCID: PMC3390039. In: Melanonychia. https://doi.org/10.1155/2012/952186 ). Discussion Our patient with homogeneous regular longitudinal melanonychia on the first nail of the left hand was treated for contact dermatitis, the lesion was recorded on the dermoscopy device and she was called for follow-up after 3 months. As in our case, melanonychia may be triggered by contact dermatitis followed by nail findings. Trauma, various infections, pregnancy, drug exposure, malignant causes may play a role in the etiology of melanonychia.