We previously reported the efficacy of ivermectin (IVM) for the treatment of 23 strongyloidiasis patients. We now reported the efficacy and safety of IVM therapy on 54 patients. Fifty-four patients, 28 males and 26 females, received a single oral dose of IVM one hour before breakfast and this treatment was repeated 2 weeks later. The following results were obtained: 1) The cure rate at 2 weeks after the initial treatment was 92.5% (49 of 53 patients) and 2 weeks after the second course was 96.0% (48 of 50 patients). 2) Four patients (7.4%) complained of diarrhea (n = 2 patients), constipation (n = 1), borborygmus (n = 1), dizziness (n = 1), diplopia (n = 1) and peri-anal itching (n = 1) after the first treatment. Three patients (5.6%) complained of borborygmus (n = 1), itching (n = 1) and exanthema (n = 1) after the second treatment. But all symptoms were mild and required no treatment and subsided in a few days. 3) Positive rate of HTLV-1 antibody was 25.9% in the patients. As described above, although side effects occurred in some cases, they were mild and transient. From these results, we concluded that IVM is an effective drug for strongyloidiasis.