Introduction: Inadequate colonoscopy bowel preparation increases procedural complications. Hypothy-roidism reduces esophageal and gastric motor activity. Investigation to determine if poor prep correlated with incidence of hypothyroidism and/or higher average thyroid stimulat-ing hormone (TSH) levels was undertaken. Methods: Data were collected on 4,200 patients from the Louisville, KY Robley Rex VA Medical Center. Specific exclusion criteria included pro-inflammatory states that are postulated to increase polyposis and pre-existing malignancies. From this group, 328 patients were found to have poor prep and 305 patients with adequate prep were randomly selected to serve as a control group. Average age of patients was 64 and 55 for poor prep and adequate prep, respectively. 306 (94%) and 271 (89%) of poor prep and adequate prep patients were males. I Inadequate bowel prep was defined as “poor” by the performing physician. Patients were hypothyroid if diagnosed and actively being treated. Maximum TSH levels were obtained. Analysis model selection was performed using a stepwise selection process where a model of best fit was produced based on Akaike information criterion (AIC). AIC estimates quality of various models, relative to each other. A Poisson regression was performed, with p-values of <0.05 being deemed statistically significant (Table 1). Figure 1 is a Forest plot of multiple logistic regression using the following variables: African-American race, Male sex, Age, Hypothyroidism, and peak TSH levels.226_A Figure 1. Patient demographics Adequate and poor prep patients with p-values.Results: 40 poor prep and 24 adequate prep patients had a diagnosis of hypothyroidism (p =0.086). The median peak TSH level was 3.1 and 2.2 for poor prep and controls, respectively, which was statistically significant (p<0.001). Multivariate regression demonstrated that TSH levels were a statistically significant factor in bowel prep quality (OR 1.08, CI 1.03-1.15, p-value= 0.010), when controlling for other variables. Conclusion: Patients with poor prep had a higher mean TSH level then controls. A larger number of patients with hypothyroidism had poor prep, but the result was not statistically significant. TSH levels had a statistically significant association with poor prep quality. However, whether or not this is physiologically significant is difficult to determine, and higher powered studies are needed. Patients with abnormal TSH levels, but who are not hypothyroid, may benefit from pre-colonoscopy treatment or intense prep regimens.226_B Figure 2. Forest Plot of multiple logistic regression with corresponding odds ratio, CI, and p-value.