The primary objective of this study is to assess the efficacy of subcutaneously administered efalizumab in the treatment of refractory, severe hydradenitis suppurativa. The secondary objectives of this study are to assess the ability to re-establish disease control after discontinuation of drug and allowance for relapse of disease, as well as to assess the safety of subcutaneously administered efalizumab in the treatment of refractory, severe hydradenitis suppurativa.