A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether asymptomatic bronchogenic cysts in adults require surgery or whether they can be adequately managed with conservative treatment or observation only. Altogether more than 310 papers were found using the reported search of which 23 represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. The papers identified included 683 adult patients with bronchogenic cysts. There was a substantial variation between the papers in the proportion of patients presenting with symptoms (6-79%), and all patients with symptoms were managed surgically. The majority of asymptomatic patients underwent empirical surgery to prevent the development of symptoms, to confirm the diagnosis and to rule out malignant transformation. A total of 74 asymptomatic patients were treated conservatively or had definitive diagnosis or treatment delayed. The longest period of observation was 22 years. In total, 33 (45%) of asymptomatic patients eventually developed symptoms requiring surgery. There was no evidence to suggest that surgery following a cyst-related complication increased the postoperative morbidity or mortality, although it was noted to increase the technical difficulty of the procedure. There were no descriptions of misdiagnosis of malignancy as bronchogenic cyst, but 5 (0.7%) of the 683 cysts studied were found to be associated with malignant cells in the cyst wall. The figures cited, however, represent only symptomatic or incidental presentations. As the prevalence of these otherwise benign entities is not known, the rates of progression to symptoms and associated malignancy may be lower than those described. We would advocate informing asymptomatic patients diagnosed with bronchogenic cyst of the 20% morbidity of surgery whether immediate or delayed, the 45% risk of developing symptoms, some of which may be serious, and the 0.7% risk of malignancy. Should patients opt for conservative management, this can be offered only if close long-term follow-up can be guaranteed.