New treatment options are required for primary systemic amyloid light chain (AL) amyloidosis. This phase 1/2 dose-escalation study aimed to determine the maximum tolerated dose (MTD) of lenalidomide in combination with melphalan and dexamethasone (M-dex), and assess the efficacy and tolerability of this therapy for patients with de novo AL amyloidosis. Twenty-six patients were enrolled across 4 cohorts: M-dex + lenalidomide 5, 10, 15, and 20 mg once daily on days 1 to 21 in a 28-day cycle. No dose limiting toxicity (DLT) was observed in cohorts 1, 2, and 3. 4. Seven patients in cohort 4, M-dex + lenalidomide 20 mg/day, experienced DLT. MTD was defined as 15 mg of lenalidomide. A complete hematologic response was achieved in 42% at the dose of 15 mg of lenalidomide per day. After a median follow-up of 19 months, estimated 2-year overall survival (OS) and event-free survival (EFS) were 80.8% and 53.8%, respectively. Hematologic and organ responses were both associated with superior EFS rates (P = .0001). A higher EFS was also observed in patients whose free light chains decreased by more than 50% during therapy (P = .019). Lenalidomide 15 mg/d + M-dex is a new effective combination therapy in patients with newly diagnosed AL amyloidosis. This study is registered at www.clinicaltrials.gov as NCT00621400.