This study aimed to 1) determine the rate of adherence to treatment recommendations from health professionals among thyroid cancer patients, 2) identify factors infl uencing the adherence, and 3) compare the quality of life among patients before and after treatment with 30 mCi. radioiodine-131 (I-131). One hundred thirty eight patients who were registered at the Nuclear Medicine Division, Songklanagarind Hospital and received I-131 ablation were enrolled in the study. The researcher interviewed the subjects on two occasions 5-7 days apart. Two instruments were used in the study: The Functional Assessment of Cancer Therapy (FACT-G) instrument for assessing the patients’ quality of life and the interview instrument developed specifi cally for the study to measure knowledge on treatmen  recommendation, knowledge on treatment, relevant health beliefs, and adherence to the treatment recommendation from health professionals. The results showed that more than 90% of patients followed the advice of health professionals on how to follow safety precautions before and after I-131 ingestion, and how to

reduce radiation risk to others. The signifi cant predictors of adherence to the recommendations of safety precautions before receiving I-131 were knowledge of the correct practices, education, and experiences with treatment. The factors affecting adherence to the recommendation of safety precautions after receiving I-131 were knowledge on safety precautions, and education. The only signifi cant predictor of adherence to the recommendation to reduce radiation was knowledge on safety precautions. The social/

family well-being significantly decreased, but emotional well-being signifi - cantly improved after I-131 treatment.