<jats:title>Abstract</jats:title><jats:sec id="S0033291719000588_sec_a1" sec-type="other"><jats:title>Background</jats:title><jats:p>The cognitive process of worry, which keeps negative thoughts in mind and elaborates the content, contributes to the occurrence of many mental health disorders. Our principal aim was to develop a straightforward measure of general problematic worry suitable for research and clinical treatment. Our secondary aim was to develop a measure of problematic worry specifically concerning paranoid fears.</jats:p></jats:sec><jats:sec id="S0033291719000588_sec_a2" sec-type="methods"><jats:title>Methods</jats:title><jats:p>An item pool concerning worry in the past month was evaluated in 250 non-clinical individuals and 50 patients with psychosis in a worry treatment trial. Exploratory factor analysis and item response theory (IRT) informed the selection of scale items. IRT analyses were repeated with the scales administered to 273 non-clinical individuals, 79 patients with psychosis and 93 patients with social anxiety disorder. Other clinical measures were administered to assess concurrent validity. Test-retest reliability was assessed with 75 participants. Sensitivity to change was assessed with 43 patients with psychosis.</jats:p></jats:sec><jats:sec id="S0033291719000588_sec_a3" sec-type="results"><jats:title>Results</jats:title><jats:p>A 10-item general worry scale (Dunn Worry Questionnaire; DWQ) and a five-item paranoia worry scale (Paranoia Worries Questionnaire; PWQ) were developed. All items were highly discriminative (DWQ <jats:italic>a</jats:italic> = 1.98–5.03; PWQ <jats:italic>a</jats:italic> = 4.10–10.7), indicating small increases in latent worry lead to a high probability of item endorsement. The DWQ was highly informative across a wide range of the worry distribution, whilst the PWQ had greatest precision at clinical levels of paranoia worry. The scales demonstrated excellent internal reliability, test-retest reliability, concurrent validity and sensitivity to change.</jats:p></jats:sec><jats:sec id="S0033291719000588_sec_a4" sec-type="conclusions"><jats:title>Conclusions</jats:title><jats:p>The new measures of general problematic worry and worry about paranoid fears have excellent psychometric properties.</jats:p></jats:sec>