Psoriasis is a complex and chronic disease, and, in most cases, therapies are required during all patients' lifetime. The efficacy and safety profiles of biological therapies are well established, but their effectiveness is still open to discussion. We performed a systematic review to summarize how the effectiveness of biological therapies for psoriasis is measured in real-world studies and to understand whether drug survival, a recent alternative outcome to clinical ones, is a recurrent and valid outcome of effectiveness. In March 2017, we searched for quantitative epidemiological data of psoriasis treatments using PubMed/Medline and EMBASE, and we included 65 publications. The retrospective study design (37%) was most frequent, followed by prospective registries (29%), prospective studies (19%), and retrospective administrative databases/claims. Drug survival was reported in over 60% of prospective registries and retrospective studies, and less frequently in prospective studies. A general consensus emerged in the definition of drug survival as the time patients remain under treatment with a specific therapy, and in its interpretation as an overall marker of treatment success and treatment adherence, as it represents simultaneously information on drug efficacy, drug safety, and patient satisfaction. In conclusion, notwithstanding some limitations, drug survival is a useful measurement of biological therapy effectiveness for psoriasis in daily practice. Its major advantage is that it can be computed also in already collected databases without any specific clinical information on psoriasis. This outcome, combined with evidence on clinical markers of effectiveness, can contribute to better understanding the performance of this expensive class of drugs.