We describe the clinical and biological features of ten patients with a survival superior to ten years (long survival), out of 175 patients diagnosed with Adult T-cell Leukemia/Lymphoma (ATL) in Martinique (1983-2013). There were 5 lymphoma and 5 chronic subtypes. Five of them (3 chronic, 2 lymphoma) had been treated with valproic acid (VA) for neurological disorders developed before or after ATL diagnosis, suggesting a beneficial role for VA as a histone deacetylase inhibitor (HDI) in ATL treatment. Total duration of uninterrupted VA treatment ranged from 8 to 37 years. Overall, the 175 incident ATL cases presented with a median survival of 5.43 months. The five VA-treated (VA(+)) patients presented with longer survival compared to VA treatment-free patients (VA(-)). For chronic subtypes, survival periods were of 213 months for 3 VA(+) patients and of 33 months for 11 VA(-) patients (p = 0.023). For lymphoma subtypes, survival periods were of 144 months for 2 VA(+) patients versus 6 months for 49 VA(-) patients (p = 0.0046). ATL cases with skin lesions, particularly lymphoma subtypes, had a longer survival (13.96 months) compared to those without skin lesions (6.06 months, p = 0.002). Eight out of the 10 patients presenting with long survival had skin lesions.