Rapid onsite evaluation (ROSE) has the potential to improve the adequacy rates of fine-needle aspiration (FNA) cytology. Studies have obtained variable results on the influence of ROSE. We conducted a systematic review and meta-analysis of studies on the influence of ROSE on FNA adequacy. We synthesized evidence across all anatomic locations. We only included studies that contained a control arm and compared cohorts with ROSE against cohorts without ROSE at a single location. We screened 2,179 studies and identified 25 studies that met our inclusion criteria. On average, ROSE improves the adequacy rate by 12%, but there was considerable variability across studies. The adequacy rate with ROSE depends on the non-ROSE adequacy rate. Sixty-five percent of the variability in the adequacy rate with ROSE was found to occur because of differences in the adequacy rate without ROSE. Studies with high non-ROSE adequacy rates showed low improvement after ROSE was implemented. Studies must account for the effect of the non-ROSE adequacy rate to determine the effect of ROSE on FNA adequacy rates.