 We will enroll 17 subjects from the age of 4 years, including adults, from multiple centers in the United States with active FMF at least 1 attack per month despite receiving at least 1.2-1.5 mgd of colchicine dose dependent on age or are intolerant of colchicine. Subjects will be diagnosed by clinical criteria with at least one heterozygote mutation of the MEFV pyrin gene. After screening subjects will be monitored for a month to observe for acute FMF attacks or if they did not develop an attack in that month until they develop two attacks. We will then use a single-subject alternating treatments design with subjects receiving in random order two 3-month courses of Rilonacept at 2.2 mgkg max 160 mg by weekly SC injection and two 3-month courses of comparable volume placebo. Subjects will continue the usual colchicine dose they were on when they started the study. Subjects with 2 acute FMF attacks during a treatment course will be able to crossover to the other treatment arm until the end of that treatment course. There will be 10 study visits: 1. Screening. 2. Treatment baseline after one month or after subjects have developed FMF attacks as described above. After 1 month of each treatment course and at the end of each treatment course overall 8 visits. At each visit subjects will return completed diary forms, used and unused drug, queried on adverse effects, undergo a physical examination and laboratory tests obtained for inflammation, safety and in some visits for translational studies. Subjects will also fill out quality of life questionnaires and give an overall estimation of the disease activity. Results will be analyzed by traditional frequency statistics using an intent to treat analysis and by Bayesian hierarchical modeling. Our primary aim is to assess the efficacy of Rilonacept in decreasing the number of acute FMF attacks while monitoring drug safety. 