Body mass index (BMI), age, and gender influence colorectal cancer (CRC) and adenoma risk. Their effects on colonoscopy characteristics are unclear, but might inform the screening approach in patient subgroups. The aims of this study were to assess the effect of BMI, age, and gender on prep quality, amount of sedation, procedure time, and adenoma prevalence for screening colonoscopy. We conducted a review of 773 eligible colonoscopies performed for average-risk CRC screening. We performed multivariable regression analyses to assess the outcomes of prep quality, amount of fentanyl and midazolam used, procedure time, and the adenoma prevalence rate (APR). Obese patients were less likely (p = 0.01) to have a good or excellent prep, had similar procedure times, and received similar amounts of fentanyl and midazolam. Increasing age had no effect on prep quality or procedure time, but was associated with decreased fentanyl and midazolam (both p ≤ 0.001). Women had similar prep quality, longer procedure times (increased by 2.8 ± 0.7 min, p < 0.001) for colonoscopies in which no polyps were detected, and received more fentanyl and midazolam (both p = 0.01). Increasing BMI, increasing age, and male gender were associated with an increased APR. The APR for women aged 50-59 with a normal BMI was 17.9 %. Normal-weight females, particularly those under age 60, have the lowest APR but have longer procedure times and require higher amounts of sedation. Screening options other than colonoscopy might be well-suited to this population.