The interest in regulatory T cells (Tregs) has been revived following the discovery of developing multiorgan autoimmune diseases as a result of depleting CD4+CD25+ T cells from mice. The importance of Tregs is being recognized in various clinical fields such as tumor and microbial immunities, transplantation and allergy. Prevalence of allergic diseases such as asthma, atopic dermatitis and rhinitis is significantly increasing worldwide. A better understanding of the mechanisms of T-cell regulation in allergic diseases may help in developing more effective therapeutic strategies. The well-known role of Tregs in preventing autoimmune diseases indicates that these important cells might be involved in prevention of allergy, and allergic diseases are associated with a low frequency and/or an impaired function of Tregs. Recent data show that natural CD4+CD25+ Tregs and interleukin (IL)-10-producing Tregs are normally able to suppress Th2 responses to allergens, while such suppression is diminished in allergic conditions. In this review, I summarize the role of Tregs in allergic diseases and discuss the possibility of manipulating these cells for treating allergic diseases.