Elevated levels of irritability have been reported across a range of psychiatric and medical conditions. However, research on the causes, consequences, and treatments of irritability has been hindered by limitations in existing measurement tools. This study aimed to develop a brief, reliable, and valid self-report measure of irritability that is suitable for use among both men and women and that displays minimal overlap with related constructs. First, 63 candidate items were generated, including items from two recent irritability scales. Second, 1,116 participants (877 university students and 229 chronic pain outpatients) completed a survey containing the irritability item pool and standardized measures of related constructs. Item response theory was used to develop a five-item scale (the Brief Irritability Test) with a strong internal structure. All five items displayed minimal conceptual overlap with related constructs (e.g., depression, anger), and test scores displayed negligible gender bias. The Brief Irritability Test shows promise in helping to advance the burgeoning field of irritability research.