Purpose: The purpose of this systematic review and meta-analysis was to assess success rates for nonvital treatment in primary teeth for caries/trauma. Methods: Databases were searched between 1960 and 2020 for randomized controlled trials, cohorts, case series, and in vitro studies. The primary outcome was overall success (clinical and radiographic) for pulpectomy and lesion sterilization tissue repair (LSTR). Included articles were independently determined, agreed upon, data extraction assessed, risk of bias, meta-analyses, and assignment of quality of evidence (GRADE). Results: Comparing teeth with and without root resorption, pulpectomy success was better (P<0.001) in teeth without preoperative root resorption. Success with pulpectomies performed with zinc oxide eugenol [ZOE] and with Endoflas (ZOE plus iodoform plus calcium hydroxide) did not differ from that observed using Vitapex or Metapex (iodoform plus calcium hydroxide; P≥0.50) after 18 months; however, Endoflas and ZOE success rates remained near 90 percent versus 71 percent or less for iodoform. Network analysis ratings showed Endoflas and ZOE performed better than iodoform alone. Also, LSTR performed better (P<0.001) than pulpectomies in teeth with preoperative root resorption, but pulpectomy results were superior (P=0.09) if roots were intact. Rotary instrumentation of root canals was significantly faster (P<0.001) than manual instrumentation. Success rates were not impacted by method of obturation or root length determination, type of tooth, number of visits, irrigants, smear layer removal, or timing/type of final restoration. Conclusions: Eighteen-month success rates support Endloflas and zinc oxide eugenol pulpectomies over iodoform pulpectomies. Lesion sterilization tissue repair had limited indication for teeth with resorbed roots.