Objective: To evaluate the extent to which a client's successful tobacco quit attempt and subsequent improvement in life satisfaction depend on the quitline counsellor assigned to provide the cessation counselling. Methods: A retrospective review of 2,944 Arizona Smokers’ Helpline client records was conducted on enrolment, follow-up, and programme treatment data. Seven month post-enrolment quit rates were calculated on an intent-to-treat sample for 30-day point prevalence during follow-up surveys. A variance components model was used to estimate counsellor effects, that is, the amount of variability in outcomes explained by individual counsellor differences. Similar analysis was done to detect presence of counsellor effects in clients’ Outcome Rating Scale (ORS) scores (Miller et al., 2003) ‒ a proxy measure of life satisfaction ‒ as they change from intake date to exit date. Results: Statistically significant differences in quit rates (2%) and ORS change scores (2%) were attributable to counsellor effects. Conclusions: The results suggest that counsellor effects have an impact on quitline outcomes that otherwise might have been overlooked if one assumed that only treatment factors and extraneous factors contributed significantly to outcomes. Additional research is required to determine the sources of counsellor effects, as well as whether additional efforts to eliminate these counsellor effects can be justified.