Retrospective review of diphencyprone in the treatment of alopecia areata. 
Contact immunotherapy with diphencyprone (DCP) is used to treat alopecia areata (AA).  Its reported efficacy is variable, and individual response cannot be predicted.  To identify patient and treatment course variables that may affect treatment outcome, and to review DCP service to identify potential areas for development and improvement.  This was a retrospective review of a DCP service over a 20-year period (1991-2010).  Complete data was available for 205 treatment courses, and 162 (79%) treatment courses were completed for 133 patients.  Overall, 72.2% (96/133) of patients had some hair regrowth (any grade).  In 15.8% of cases (21/133), response was > 90% regrowth.  However, 27.1% (36/133) had no response.  We found that extent of alopecia at baseline and duration of disease were statistically significant when comparing patients with an optimal outcome to those without (P < 0.05).  In contrast to other reports, atopy, age at onset and nail dystrophy were not statistically significant.  For patients receiving more than one course, response to DCP treatment was broadly consistent.  Extent of alopecia at baseline and duration of disease are important factors in predicting response.  Our results suggest that atopy should not be considered a predictor of poor outcome with respect to DCP treatment.  A need for improved data collection, particularly regarding longer-term outcomes, was identified.  The role of maintenance therapy requires objective assessment.  Opportunities for DCP self-administration by patients should be explored.  Limitations of this study include the retrospective nature of the review and lack of long-term follow-up data.