['Phototherapy may be effective in atopic dermatitis (AD). Medium-dose (MD) ultraviolet (UV) A1 was introduced for the treatment of AD. Few immunohistochemical data are available pertaining to phototherapy in AD. Regulatory T cells may play a role in clearing AD.', 'We sought to compare the clinical and immunohistochemical effects of narrowband (NB) UVB and MD UVA1 treatment in patients with AD.', 'Thirteen adult patients with AD were included in this randomized investigator-blinded half-sided comparison study between NB UVB and MD UVA1. Disease activity was measured using the Leicester sign score. Skin biopsy specimens were taken before and after phototherapy. Regulatory T cells were stained with the forkhead box protein P3 (FoxP3).', 'NB UVB and MD UVA1 both significantly decreased AD severity (P < .01) and the dermal cellular infiltrate. The percentage of FoxP3(+)CD3(+) T cells did not change after NB UVB or MD UVA1 treatment.'] Are narrowband ultraviolet B and medium-dose ultraviolet A1 equally effective in the treatment of moderate to severe atopic dermatitis?