A 78-year-old woman was diagnosed with multiple myeloma (MM: IgG κ type, stage IIIA, ISS III) at a nearby hospital in August 2010. High-dose dexamethasone therapy was ineffective, and she was treated with 2 courses of bortezomib. She was referred to our hospital with back pain and dyspnea in November. She was diagnosed with interstitial pneumonia (IP) and improved rapidly with steroid pulse therapy. Because the involvement of bortezomib was suspected in IP, lenalidomide therapy was selected for MM. Lenalidomide (15 mg) was administered for 2 courses. The patient achieved a PR and the treatment is still ongoing with a good response. According to the interim report on PMS (post-marketing surveillance), 3 of the 1,177 patients treated with lenalidomide developed IP. The dose level was 25 mg in 2 cases and 10 mg in 1 case. The outcomes of these patients were death in 1 case, not recovered in 1 case, and unknown in 1 case. When lenalidomide is used to treat bortezomib-induced IP, there are no rules or regulations about its dose level. In the present case, the dose of lenalidomide (15 mg) was based on the retreatment dose after bone marrow suppression. Low-dose lenalidomide therapy was effective and safe against MM with a bortezomib-associated lung disorder.