Background and Objective: Little research exists which investigates the contextual factors and hidden influences that inform surgeons and surgical teams decisionmaking in preoperative assessment when deciding whether to or not to operate on older adult prostate cancer patients living with aging-associated functional declines and illnesses. The aim of this study is to identify and examine the underlying mechanisms that uniquely shape preoperative surgical decision-making strategies concerning older adult prostate cancer patients.Methods: Qualitative methodologies were used that paired ethnographic field observations with semistructured interviews for data collection. An inductive thematic analysis approach was used to identify, analyze, and describe patterns in the data.Results: Factors underlining surgical decision-making originated from the context of two categories: (1) clinical and surgery-specific factors; and (2) non-patient factors.Thematic subcategories included personal experiences, methods of assessment during medical encounters, anticipation of outcomes, perceptions of preoperative assessment instruments for frailty and multimorbidity, routines and workflow patterns, microcultures, and indirect observation and second-hand knowledge.Conclusion: Surgeon's personal experiences has a significant impact on the decisionmaking processes during preoperative assessments. However, non-patient factors such as institutional microcultures passively and actively influence decision-making process during preoperative assessment. K E Y W O R D S frailty, medical decision-making, multimorbidity, older adults, preoperative assessment, prostate cancer, surgical assessment 1 | INTRODUCTION Prostate cancer is the second most common form of cancer diagnosed among men in the United States. 1 It is projected that there will be 164 690 new cases and 29 430 deaths in 2018 as a result of the disease, 2and older men represent the majority of prostate cancer diagnoses and mortalities. 3 In general, radical prostatectomy is considered one of the primary treatments available with curative intent for men diagnosed with clinically localized prostate cancer and a life expectancy of more than 10 years. 4-8 Given that older adults (defined herein as age 65 years or more 9,10 ) account for a significant ratio of the patient population, special attention and consideration must be given by surgeons and surgical teams during the stages of preoperative assessment when deciding whether or not to operate.However, the decision to operate in older adults is a complex task since the rate of adverse postoperative outcomes increases How to cite this article: Kierkegaard P, Vale MD, Garrison S, Hollenbeck BK, Hollingsworth JM, Owen-Smith J.Mechanisms of decision-making in preoperative assessment for older adult prostate cancer patients-A qualitative study.