Splinter nail haemorrhages are thin, non-blanchable, longitudinal stripes beneath the nail plate that can appear red, brown, or black. Dermoscopic examination enhances visualization of these lines, which result from ruptured capillaries in the nail bed, with the blood integrating into the nail plate and moving distally as the nail grows. Common causes include trauma, skin and systemic diseases (e.g., psoriasis, connective tissue disorders), infections like endocarditis, and medication use. This case report highlights a 72-year-old female with Sézary syndrome who developed drug-induced splinter nail haemorrhages following treatment with brentuximab vedotin. The patient initially presented with erythroderma, palmoplantar keratoderma, and lymphadenopathy, later progressing to stage IVB disease. Nail changes, manifesting as painful band-like longitudinal streaks on all nail plates, were observed after the 15th treatment cycle. These lesions, distinct from the broader nail changes typical of Sézary syndrome, correlated with the administration of brentuximab and advanced disease progression. The findings underscore the importance of monitoring nail lesions as potential markers of treatment efficacy and disease prognosis in Sézary syndrome.