Background: Peripheral T-cell lymphomas (PTCL) account for 10-15% of lymphomas. They share an aggressive clinical behaviour and a poor prognosis when treated by CHOP-like regimen which is nevertheless consider as a standard because others regimens failed to demonstrate survival advantage. Romidepsin is a histone deacetylase inhibitor with promising results in PTCL. First trials showed a response rate of 38% in heavily pre-treated PTCL patients. These results were confirmed with 15% of patients reaching a CR/CRu, 89% of them without disease progression at 13 months. Adverse events include gastrointestinal, hematologic and asthenic conditions. A phase I study of romidepsin combined with CHOP was conducted by LYSA. A total of 18 patients were included. The recommended dose was 12 mg/m² administered at day 1 and day 8 of each cycle. Methods: Ro-CHOP study is an international phase III study comparing 6 cycles of CHOP21 with 6 cycles of romidepsin-CHOP21 (EUDRACT 2012-001580-68). Primary endpoint is Progression-Free Survival assessed independently. Secondary objectives include overall survival, other efficacy parameters, analysis of response rate according to ¹⁸FDG-PET, safety, quality of life and biological ancillary studies. A total of 420 subjects aged from 18 to 80 years will be enrolled in the study. Main inclusion criteria are untreated PTCL whatever Ann Arbor stage and a performance status of 0-2. Main exclusion criteria are other subtypes of lymphoma, HTLV1 positivity, any cardiac abnormality, poor renal, hepatic and marrow functions unless related to lymphoma. Patients are randomized 1:1 between the two regimens. A stratification is performed with IPI score, age and histology. The first patient has been included in January 2013. A recruitment of 10.5 patients per month is anticipated, with a total duration of the study of 60 months. An update on enrolment will be presented at the meeting. Clinical trial information: 2012-001580-68.