BACKGROUNDTherapeutic options to treat atopic dermatitis are limited. Leukocytes from atopic patients have an abnormally high activity of cyclic adenosine monophosphate (AMP)-phosphodiesterase (PDE), which can be normalized in vitro by PDE inhibitors. Cipamfylline is a new potent and selective inhibitor of PDE-4.OBJECTIVESTo compare the efficacy and safety of up to 14 days' topical treatment with cipamfylline (0.15%) cream with vehicle and with hydrocortisone 17-butyrate (0.1%) cream.PATIENTS AND METHODSInternational, multicentre, prospective, randomized double-blind, left-right studies of cipamfylline vs. vehicle and cipamfylline vs. hydrocortisone 17-butyrate in adult patients with stable symmetrical atopic dermatitis on the arms.RESULTSBoth cipamfylline and hydrocortisone 17-butyrate reduced the Total Severity Score significantly (P < 0.001). The reduction with cipamfylline was significantly greater than that with vehicle (difference vehicle-cipamfylline 1.67 95% confidence interval (CI) 1.06, 2.28; P < 0.001) and was significantly less than with hydrocortisone 17-butyrate (difference hydrocortisone-cipamfylline -2.10 95% CI -2.93, -1.27; P < 0.001). Investigator and patient assessments of the overall treatment response showed a similar picture.CONCLUSIONSCipamfylline cream is significantly more effective than vehicle, but significantly less effective than hydrocortisone 17-butyrate cream in the treatment of atopic dermatitis.