This was a multi-center, two-part, double-blind, placebo-controlled study (Parts A and B) designed to assess the efficacy, safety, and tolerability of weekly subcutaneous (SC) doses of 160 mg of rilonacept in adult subjects with active CAPS. These phases were followed by extended open-label phases. After written informed consent was obtained, subjects who met the protocol eligibility criteria were enrolled at one of 27 study sites in the United States. The study consisted of a 3-week screening period preceding Part A, a 6-week long double-blind, randomized phase of the study. All subjects were then treated with single-blind rilonacept for 9-weeks, followed by a subsequent 9-week, double-blind, withdrawal phase during which subjects were re-randomized to either rilonacept or placebo. Subjects then continued treatment in a 24-week open-label extension phase (OLE) and a further 112-week long-term open-label extension (LTOLE), during which all subjects received rilonacept and a 6-week post-treatment follow-up period. Amendments 4 and 6 allowed eligible adult and pediatric subjects aged 7 and above to enroll directly into the open-label phases of the trial.