Large numbers of passengers and large amounts of goods are transported by air every year. This attracts the interest of terrorists, which poses high demands on aerodrome security. Technological solutions, and rules and regulations, have been widely implemented to detect security threats, but there is also a need for leading security indicators. Safety culture and climate have been identified as such leading indicators. The aim of this study was to develop and test a questionnaire instrument to measure aerodrome security climate. The development contained an expert focus group, expert panel, two pilot tests at four and five airports, respectively, and one fullscale study at nine Swedish commercial airports. The final instrument comprised 12 dimensions grounded in previous safety culture and climate research, and targeting three organizational levels. It had good psychometric properties and was validated against compliant as well as participative security behavior. We believe ADSECQ is suitable to evaluate the aerodrome security climate standard, pinpoint security climate areas for improvement, and evaluate the effect of interventions.