Background and study aims There are limited longitudinal data regarding detection rates for sessile serrated adenoma/polyps (SSADR) and right-sided hyperplastic polyps (RHPDR) that constitute the proximal serrated lesion detection rate (PSLDR). Recently, a minimum PSLDR of 4.5 % has been suggested. This study was designed to assess SSADR, PSLDR and adenoma detection rate (ADR) for a newly qualified gastroenterologist and compare them to published data and to assess the change in SSADR, PSLDR and ADR over time for potential improvement with experience. Patients and methods All colonoscopies performed by a single colonoscopist (AM), at one Australian ambulatory direct-access endoscopy center over 4 years from 2011 to 2015 were retrospectively analyzed. Histology was reported by a single expert pathologist (SL). ADR, SSADR, RHPDR and PSLDR were recorded. Results A total of 841 colonoscopies were performed on 637 patients. Of them, 454 (54 %) were males. Mean age was 59 years. Of the colonoscopies, 87 % were performed for patients with ASA scores of 1 – 2, 422 (50.2 %) were for screening or surveillance, 374 (44.5 %) for investigation of symptoms and 45 (5.4 %) had therapeutic indications. Conventional adenomas were detected in 346 colonoscopies (ADR = 41.1 %), SSA/P in 124 (SSADR = 14.7 %) and RHP in the absence of SSA/P in 35 (RHPDR = 4.2 %). PSLDR was 18.9 %. ADR was stable over time (range 33 %-50 %). SSADR and PSLDR increased over time [SSADR: 8.6 % (2011), 8.4 % (2012), 14.9 % (2013), 18.5 % (2014), 25.0 % (2015); PSLDR: 10.5 % (2011), 11.3 % (2012), 16.8 % (2013), 27.2 % (2014), 29.4 % (2015)]. There was a statistically significant improvement in SSADR (IRR 1.37) and PSLDR (IRR 1.36) over the study period ( P < 0.001), whereas the ADR remained stable (IRR 1.04, P = 0.334). Conclusions SSADR and PSLDR in this unselected direct-access cohort are high and exceed previously reported detection rates in the final 2 years. Detection rates improved with experience, likely representing a learning effect. The minimum expected PSLDR may need to be revised upwards and further studies are required, particularly in areas where screening colonoscopies are offered only for patients with increased colorectal cancer risk (family history or fecal immunochemical test-positive).