Background. Use of radioactive iodine (RAI) ablation has been reported to vary significantly between studies. We explored variation in RAI ablation care patterns between seven thyroid cancer treatment centers in Canada.Methods. The Canadian Collaborative Network for Cancer of the Thyroid (CANNECT) is a collaborative registry to describe and analyze patterns of care for thyroid cancer. We analyzed data from seven participating centers on RAI ablation in patients diagnosed with well-differentiated (papillary and follicular) thyroid cancer between 2000 and 2010. We compared RAI ablation protocols including indications (based on TNM staging), preparation protocols, and administered dose. We excluded patients with known distant metastases at time of RAI ablation.Results. We included 3072 patients. There were no significant differences in TNM stage over time. RAI use increased in earlier years and then declined. The fraction of patients receiving RAI varied significantly between centers, ranging between 20–85% for T1, 44–100% for T2, 58–100% for T3, and 59–100% for T4. There were significant differences in the RAI doses between centers. Finally, there was major variation in the use of thyroid hormone withdrawal or rhTSH for preparation of RAI ablation.Conclusion. Our study identified significant variation in use of RAI for ablation in patients with well-differentiated thyroid cancer both between Canadian centers and over time.