Lenalidomide treatment in combination with dexamethasone and/or chemotherapy is associated with a significant risk of venous thromboembolism (VTE) in patients with multiple myeloma (MM). However, the incidence of asymptomatic VTE in lenalidomide-treated MM patients remains unclear. A total of 80 relapsed and refractory MM patients treated with lenalidomide-containing regimens in a single institution between July 2010 and July 2014 were retrospectively analyzed. Of these, eight patients had asymptomatic VTE before starting lenalidomide. The remaining 72 patients received thromboprophylaxis with low-dose aspirin (100 mg daily) and monitoring of plasma D-dimer levels on each visit. During the median follow-up time of 7.3 months (range 1.0-43.5 months), 29 patients (40.3 %) showed an elevation of D-dimer (≥2.5 μg/mL), and 13 (18.1 %) showed asymptomatic VTE in a lower extremity. Median time to asymptomatic VTE events from initiation of lenalidomide treatment was 3.0 months (range 1.0-13.1 months). All patients having an asymptomatic VTE continued lenalidomide treatment on warfarinization (target international normalized ratio 1.5-2.5), and none of them developed symptomatic VTE. In conclusion, an asymptomatic VTE event occurred in 18 % of Japanese MM patients receiving lenalidomide-containing therapy despite aspirin prophylaxis. Serial monitoring of plasma D-dimer levels and early intervention may help to prevent symptomatic or lethal VTE events.