Objectives: Evaluation of the periodontal status is necessary prior to management with high-dose chemotherapy before hematopoietic stem cell therapy (HSCT). During medical therapy, pre-existing periodontal conditions may exacerbate and cause local and systemic complications. When possible, maximal oral health should be achieved prior to engraftment. In this study, we aimed to determine the alterations occurred in the periodontal status of the patients after periodontal treatment and allogenic HSCT and evaluate the effect of intensive periodontal approach on the short-term complications of HSCT. Methods: The alterations occurred in the periodontal tissues 34weeks after periodontal treatment and after HSCT periods of 3months for 29 patients treated with full-mouth periodontal treatment completed in 24h in addition to eradication of dental foci, and oral hygiene status were evaluated using pocket depth measurements, presence of bleeding on probing and plaque and gingival indices. The incidence and severity of acute graft-versus-host disease (GVHD) and oral mucositis (OM) were recorded. Duration of engraftment period and the episode of febrile neutropenia were also evaluated. Results: There were significant improvements in periodontal status after periodontal treatment (P<0.001). There were 14 (48.3%) patients without acute GVHD and 17 (58.6%) patients with no sign of OM. The majority of OM was at grade II level. There was a negative relation that exists between the percentage of BOP (+) sites and presence of OM (r=0.518, P<0.05). Conclusions: Together with a significant reduction in gingival inflammation and maintenance of the improvement in periodontal health, remarkable decrease in the incidence and severity of OM were observed.