CONTEXT: Management of non-muscle-invasive bladder cancer (NMIBC) is costly and associated with negative health-related quality-of-life effects, in part because of the frequent need for repeated transurethral resections under general/regional anaesthesia. Outpatient-based diathermy or laser ablation is another option, but evidence for its efficacy is mixed and its use is controversial. OBJECTIVE: To systematically review evidence regarding the efficacy and safety of outpatient diathermy and laser ablation for the treatment of recurrent NMIBC. EVIDENCE ACQUISITION: The EMBASE, MEDLINE/PubMed, and Cochrane Library were searched from inception to June 26, 2020. All studies evaluating the use of diathermy or laser ablation for bladder tumours (new or recurrent) in an outpatient setting under local anaesthetic were included. Two reviewers independently screened all articles, searched the reference lists of retrieved articles, and performed the data extraction. The quality of evidence and risk of bias were assessed using the GRADE and ROBINS-I tools. EVIDENCE SYNTHESIS: The search yielded 1328 studies. After excluding duplicates, 1319 titles and abstracts were screened and 17 studies (1584 patients) were eligible for inclusion in the final review. The majority of patients had small, low-grade tumours, but there was heterogeneity in the inclusion criteria. Overall, laser ablation and diathermy resulted in mean recurrence rates of 47% and 32% at follow-up of 22-38 mo, respectively, with a mean progression rate of 3-12% (low certainty of evidence). Both procedures were well tolerated, with low pain scores and low periprocedural complication rates (moderate certainty of evidence). CONCLUSIONS: Outpatient diathermy and laser ablation have good short-term efficacy in patients with low-grade NMIBC and reduce the need for intervention under general/regional anaesthesia. The procedures are well tolerated with low complication rates. The overall certainty of evidence is low, with heterogeneity between studies and methodological limitations. However, we have highlighted the need for randomised trials with long-term follow-up using standardised risk classification and outcome measures. Despite these limitations, the findings will aid in patient counselling regarding this less invasive treatment option that avoids the morbidity of transurethral resection. PATIENT SUMMARY: Outpatient diathermy and laser ablation have good success rates in treating recurrent low-grade bladder tumours in the short term, avoiding the need for more invasive procedures under general/regional anaesthesia, with low rates of side effects. Further studies are needed to determine whether these treatments remain safe and effective in the long term.