Objectives Medication adherence with urgency urinary incontinence (UUI) treatment is challenging and the best assessment methodology is uncertain. We sought to describe adherence with anticholinergic (AC) versus placebo (P) by comparing pill counts and MEMSCAP event data and to identify factors associated with adherence. Methods The randomized controlled AC versus Botox Comparison trial of women with moderate to severe idiopathic UUI included 126 participants initiating AC plus P bladder injection and 121 receiving P pills plus Botox injection. Adherence data on 243 participants (124 AC and 119 P) were calculated by pill count and MEMSCAP data for each 2-month interval during the 6-month study that allowed for dose escalation/drug change. Overall composite adherence estimates were calculated using the average of both methods and weighted by the duration of each 2-month interval. Results Treatment groups had no significant differences in dosing duration (P = 0.76) or mean adherence (AC, 83.3% [16.8] vs P, 84.8% [13.8]). Only 53% of women met the dichotomous outcome of more than 80% adherence during all intervals. Correlation between adherence by pill counts versus MEMSCAP decreased over time with pill counts demonstrating higher adherence than MEMSCAP (r = 0.53, 0.50, and 0.36 for each 2-month interval). Lower adherence was associated with higher baseline incontinence severity and better UUI quality of life for the AC group and with current smoking status in both groups. Conclusions Adherence using pill counts and MEMSCAP was reasonably correlated and similar in both the AC and P groups. In the AC group, higher baseline incontinence severity and better UUI Quality of Life were associated with decreased adherence. Smokers were less adherent.