OBJECTIVES: Late presentation and delays in diagnosis and treatment consistently translate into poor outcomes in sub-Saharan Africa (SSA). The aim of this study was to collate and appraise the factors influencing diagnostic and treatment delays of adult solid tumours in SSA. DESIGN: Systematic review with assessment of bias using Risk of Bias in Non-randomised Studies of Exposures (ROBINS-E) tool. DATA SOURCES: PubMed and Embase, for publications from January 1995 to March 2021. ELIGIBILITY CRITERIA: Inclusion criteria: quantitative or mixed-method research, publications in English, on solid cancers in SSA countries. EXCLUSION CRITERIA: paediatric populations, haematologic malignancies, and assessments of public perceptions and awareness of cancer (since the focus was on patients with a cancer diagnosis and treatment pathways). DATA EXTRACTION AND SYNTHESIS: Two reviewers extracted and validated the studies. Data included year of publication; country; demographic characteristics; country-level setting; disease subsite; study design; type of delay, reasons for delay and primary outcomes. RESULTS: 57 out of 193 full-text reviews were included. 40% were from Nigeria or Ethiopia. 70% focused on breast or cervical cancer. 43 studies had a high risk of bias at preliminary stages of quality assessment. 14 studies met the criteria for full assessment and all totaled to either high or very high risk of bias across seven domains. Reasons for delays included high costs of diagnostic and treatment services; lack of coordination between primary, secondary and tertiary healthcare sectors; inadequate staffing; and continued reliance on traditional healers and complimentary medicines. CONCLUSIONS: Robust research to inform policy on the barriers to quality cancer care in SSA is absent. The focus of most research is on breast and cervical cancers. Research outputs are from few countries. It is imperative that we investigate the complex interaction of these factors to build resilient and effective cancer control programmes.