There is little evidence regarding the maintenance of long-term clinical remission by adalimumab (ADA) therapy in Crohn's disease (CD) patients naïve to anti-tumor necrosis factor treatment (naïve CD patients), since most CD patients are treated with ADA after infliximab (IFX) therapy. The long-term clinical response to ADA was retrospectively analyzed in 17 naïve CD patients for at least 24 months, and the serum trough IFX levels were evaluated in patients switching from ADA to IFX. Of the 17 naïve CD patients, 14 (82.4%) maintained long-term clinical remission with ADA therapy for at least 24 months, without serious adverse events. The clinical condition of 7 patients was observed for more than 36 months, and 3, 1, 1, and 2 cases maintained remission at months 42, 48, 54, and 60 after ADA therapy, respectively. Three patients (17.6%) switched from ADA to IFX less than 24 months after the start of ADA therapy, and they had remission, retaining trough levels of IFX higher than 1 μg/ml, occasionally by dose escalation. In conclusion, maintenance ADA therapy achieves long-term clinical remission in naïve CD patients. Switching from ADA to IFX is an important therapeutic option in CD patients showing loss of response to ADA, occasionally with dose escalation, based on the analysis of serum IFX trough levels.