BACKGROUND Anal abscess and perianal fistula is a high prevalence disorder in general population that affect adult patients on young ages, affecting them significantly their social and quality of life. There is clinical evidence that the origin of most perianal fistulas (60%) is with an episode one year before of a perianal abscess. In fact, the established cryptoglandular hypothesis considered the origin of anal fistula, a chronic infectious disease starting on a clinical episode of an anal glands abscess. However, controversy exists regarding the role of antibiotics in the development of anal fistula after incision and drainage of perianal abscess. Nowadays, only two single-centre randomized controlled trials has been published addressing this issue, with inconclusive results. The MAIN OBJECTIVE of the study is to examine the clinical benefit of antibiotic therapy in patients with a perianal abscess, to avoid the development of a perianal fistula. METHODOLOGY We designed a prospective, multicentre double-blind placebo trial to analyse the clinical benefit of a course of antibiotics after perianal abscess drainage to diminish the probability of development of perianal fistula in the follow up of patients. Patients with anal abscess will be allocated randomly either to receive 7 days of oral metronidazole/ciprofloxacin in addition to their standard care or to receive standard care and placebo, after they will be discharged from the hospital. Patients will be followed clinically at different intervals during one year in order to know if they develop anal fistula. Also a quality of life assessment at the end of the study will be evaluated. EXPECTED RESULTS We expected that patients allocated to antibiotic treatment would develop a significant less anal fistulas in their follow-up with a related significant better quality of life. Thus, a change on standard of care led by our group, may be achieved.