Extracorporeal photopheresis (ECP) is a safe treatment modality with immunomodulatory effects. The latter may also explain efficacy of ECP in patients with atopic dermatitis (AD). We aimed to assess various blood parameters of AD patients who underwent ECP over a maximum 1-year treatment period. We performed a retrospective single-center chart review (clinical data, laboratory data) of adult patients with AD who had received for at least 3 ECP cycles, in part combined with other treatment modalities. We studied 60 patients with AD (85% extrinsic type, 15% intrinsic type) who had median number of 14 (4-23) ECP cycles within a maximum 1-year treatment. When compared with baseline, leukocytes and lymphocytes remained significantly decreased after 3-, 6-, 9-, and 12-month ECP ( P = 0.014 and P = 0.0012, respectively). A significant decline of eosinophils, as well as eosinophilic cationic protein levels, was observed after 3-, 6-, 9-, and 12-month ECPs ( P = 0.011 and P = 0.0017, respectively). Total serum immunoglobulin E (IgE), as well as lactate dehydrogenase, were significantly decreased at 3-, 6-, 9-, and 12-month evaluation compared with baseline ( P < 0.00001 and P = 0.00007, respectively). Patients with slight or marked improvement of AD after their ECP treatment period had significantly higher median baseline serum IgE levels than patients who did not respond to ECP ( P = 0.0023). Several laboratory parameters, including eosinophils, eosinophilic cationic protein, total serum IgE, and lactate dehydrogenase, which declined under ECP, are well-known disease biomarkers for AD patients. With normalization of the abovementioned laboratory parameters, a clinical response to ECP treatment was observed in almost two thirds of patients, confirming that ECP may be an effective combination treatment modality for AD.