Subungual melanoma (SUM) is an uncommon form of cutaneous melanoma, accounting for approximately 0.7% to 3.5% of cases in the Caucasian population. This type of melanoma most frequently occurs on the thumb and the hallux. Its most common clinical presentation is the appearance of longitudinal melanonychiaA 65-year-old fair-skinned woman with no relevant medical history presented with a two-month history of longitudinal melanonychia on the right hallux. The lesion measured approximately 2 mm in width at its central portion and 3 mm at the base, and distal onycholysis was noted, together with an early Hutchinson’s sign on the proximal nail fold. Given these findings, an urgent dermatology referral was requested, and a nail bed biopsy was performed. Histopathological examination confirmed acral lentiginous melanoma with a Breslow thickness of 0.7 mm. The patient is currently awaiting surgery for complete excision of the tumor with appropriate margins, and the tumor board is evaluating the need for a sentinel lymph node biopsy due to the aggressive nature of this histological subtype.An unusual case due to the very early detection of a rare subungual melanoma, with an initial Hutchinson sign and low Breslow thickness. It differs from the literature because of its early presentation and the rapid coordination between primary care and dermatology.Early detection of suspicious melanonychia and prompt referral from primary care enable diagnosis of subungual melanoma at an early stage, improving the patient’s prognosis.Subungual melanoma is an uncommon neoplasm with a poor prognosis, typically presenting as longitudinal melanonychia, sometimes accompanied by Hutchinson’s sign. In this context, early recognition of these signs in primary care is crucial, as urgent referral enables earlier diagnosis and improves outcomes. As in our case, definitive diagnosis requires histopathological confirmation through a nail bed biopsy.The treatment of melanoma depends on the stage of the disease and, in early phases, may range from local surgical excision to radical amputation of the phalanx. The staging workup includes imaging studies and sentinel lymph node biopsy, both essential for assessing potential local or distant spread. Keywords: Melanoma; Biopsy; Dermatology