Basal cell carcinoma (BCC) is the commonest cancer affecting white-skinned individuals, and worldwide incidence is increasing. Although rarely fatal, BCC is associated with significant morbidity and costs.To assess the effects of interventions for primary BCC in immunocompetent adults.We updated our searches of the following databases to November 2019: Cochrane Skin Group Specialised Register, CENTRAL, MEDLINE, Embase, CINAHL, and LILACS. Certainty of evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) method. We used standard methodological procedures expected by Cochrane.We included 52 RCTs with 6990 participants (median age 65 years, range 20-95). Mean study duration was 13 months (range 6 weeks to 10 years). Ninety-two percent (48/52) of studies exclusively included histologically low-risk BCC (nodular and superficial subtypes). The certainty of evidence was predominantly low or moderate for the outcomes of interest. Overall, surgical interventions have the lowest recurrence rates, and there may be slightly fewer recurrences with MMS over SE for primary, facial BCC (high-risk histological subtype or located in the 'H-zone' or both) (low-certainty evidence). Non-surgical treatments, when used for low-risk BCC, are less effective than surgical treatments, but recurrence rates are acceptable and cosmetic outcomes are probably superior.Surgical interventions have lower recurrence rates and remain the gold-standard for high-risk BCC. Of the non-surgical treatments, topical imiquimod has the best evidence to support its efficacy for low-risk BCC. Priorities for future research include agreement on core outcome measures and studies with longer follow-up.