Akathisia is a common side-effect of dopamine receptor D2 antagonists that often remains undiagnosed. Conventional diagnostic and grading instruments are cumbersome and can be difficult to remember and to use. To facilitate the Emergency Department (ED) assessment of acute drug-induced akathisia, I sought to derive and evaluate a simplified instrument using the database compiled from three prior studies of acute drug-induced akathisia. These studies had used a conventional Long instrument in the prospective assessment of 360 adult ED patients aged 17-65 years who received intravenous prochlorperazine (10 mg) in the treatment of headache or nausea and vomiting. The Short instrument was derived from the Long instrument using the Wilcoxon z-test to identify the individual findings most strongly associated with the diagnosis of akathisia. I then retrospectively applied the Short instrument to the cohort and used pairwise analyses to compare results obtained from both instruments. Sensitivity, specificity and receiver operating characteristic curves were used to analyze the impact of instrument form on diagnostic accuracy. The Long criteria diagnosed akathisia in 118 (32.8%; 95% confidence interval [CI] 28.0%-37.9%) patients and the Short diagnosed akathisia in 120 (33.3%; 95% CI 28.5%-38.5%). When akathisia was characterized categorically as either absent or present, the Short criteria agreed with the Long in 358 cases (99.4%; 95% CI 98.0%-99.9%). Treating the diagnoses established by the Long criteria as the gold standard, the Short instrument had a sensitivity of 100.0% (95% CI 96.9%-100%) and a specificity of 99.2% (95% CI 97.0%-99.9%). Regarding the accuracy of categorizing akathisia into four severity grades, the Short scale agreed in 325 of 360 cases (90.3%; 95% CI 86.7%-93.1%) and misgraded 35 cases (9.7%; 95% CI 6.9%-13.3%), 34 of which fell within one grade of the Long scale. The Short instrument is highly accurate in diagnosing acute drug-induced akathisia, in comparison with the Long criteria, in the ED setting. The Short instrument also provides fairly accurate grading of akathisia severity. This simplified instrument should facilitate the detection and treatment of akathisia in the ED.