Purpose: It is well recognized that gingival enlargement is induced by unwanted effect associated with three major drugs/drug groups - phenytoin, cyclosporine, and the calcium channel blockers. The present case report describes the effect and limitation of non-surgical treatment in gingival enlargement cases. Materials and methods: Three cases included 2 drug-influenced gingival enlargement patients and a idiopathic gingival fibromatosis patient. For the drug-influenced gingival enlargement patients, the medication was replaced with other medication. And then, all the patients were treated non-surgically. Results: Drug-influenced gingival enlargements had been reduced after non-surgical treatment and the results were well-maintained. In the idiopathic gingival fibromatosis case, non-surgical treatment resulted in only limited reduction of gingival enlargement, and surgical periodontal treatment was unavoidable. Conclusion: These case reports indicated that non-surgical periodontal treatment with change in medication was effective in the treatment of drug-influenced gingival enlargements. Non-surgical approach can be considered as the primary management to reduce the gingival enlargement. If non-surgical treatment encounters a limitation, surgical treatment should be considered.