Background: Studies evaluating smoking cessation treatment outcomes in cancer patients are scarce, despitesmoking cessation importance in cancer care. We sought to add to the literature by evaluating smoking cessationin a challenging group of cancer patients (medium-to-heavy smokers) visiting an out-patient smoking cessationclinic (SCC) in a cancer center in Amman, Jordan. Materials and Methods: Patients smoking >9 cigarettes perday (CPD) and referred to the SCC between June 2009 and May 2012 were studied. Clinic records were reviewedto measure demographic and baseline clinical characteristics, and longitudinal (3-, 6- and 12- month) followupby phone/clinic visit was conducted. At each follow-up, patients were asked if they experienced medicationside-effects, if they had returned to smoking, and reasons for failing to abstain. Descriptive and multivariablelogistic regression analyses were performed. Results: A total of 201 smokers were included in the analysis. The3-month abstinence was 23.4% and significantly associated with older age, being married, and presenting withlower (≤10ppm) baseline carbon monoxide (CO) levels. On a multivariable level, lower CO levels, a higher income(relative to the lowest income group), being older, and reporting severe dependence (relative to dependencereported as ‘somewhat’ or ‘not’) were significant predictors of higher odds of abstinence at three months.Reasons for failing to quit included not being able to handle withdrawal and seeing no value in quitting. LongtermARs did not reach 7%. Conclusions: In a sample of Jordanian smokers (>9CPD) with cancer and receivingsmoking cessation treatment, ARs were low and further declined with time. Results underscore the need formore aggressive patient management and rigorous follow-up during and after smoking cessation treatment,particularly when this takes place in challenging settings. Observed reasons for failure to abstain should be usedto tailor counseling practices.