OBJECTIVES: This article reports the psychometric properties of two new condition-specific questionnaires: 1) the 18-item Underactive Thyroid-Dependent Quality of Life Questionnaire (ThyDQoL) individualized measure of perceived impact of hypothyroidism on quality of life (QoL); and 2) the 15-item Underactive Thyroid Symptom Rating Questionnaire (ThySRQ), in which patients rate symptom bother. METHODS: A cross-sectional survey was conducted of 110 adults with overt and subclinical hypothyroidism, 103 treated with thyroxine. Patients, the majority of whom (81%) were women, were recruited from primary care (57%) and from hospital clinics (43%). The mean age of patients was 55.1 (SD 14.3) years. Respondents rated personally applicable ThyDQoL life domains for importance and impact of hypothyroidism, and ThySRQ symptom bother. RESULTS: Completion rates were high (>98%). All 18 ThyDQoL domains were rated as negatively impacted by hypothyroidism and important for QoL. The ThyDQoL had high internal consistency reliability (Cronbach's alpha = 0.949 [N = 97]), factor analysis indicated that applicable domains could be combined into an overall Average Weighted Impact score, for which the sample mean, -3.11 (2.2), showed considerable negative impact of hypothyroidism on QoL (maximum possible range -9 to +3). There is good preliminary evidence to justify shortening the ThyDQoL to 14 domain-specific items. For the ThySRQ Cronbach's alpha was 0.808 (N = 95). Highest symptom bother ratings were for hair problems, weight gain, depression, cold, and tiredness. CONCLUSIONS: Both the ThyDQoL and ThySRQ are highly acceptable to patients with hypothyroidism and have good internal consistency reliability. Their sensitivity to change now needs to be evaluated in clinical trials.