Abstract: The invention relates to a workpiece testing method, in particular for testing workpieces (5) for internal defects (6), for example workpieces (5) made of fiber-reinforced plastic, comprising the following steps: applying ultrasonic waves (9, 19) to a workpiece (5), detecting ultrasonic signals (10, 20) generated by applying the ultrasonic waves (9, 19) to the workpiece (5), and generating ultrasonic tomogram data of the workpiece (5) from the ultrasonic signals (10, 20). The invention is characterized in that the workpiece (5) is machined, in particular milled, and the ultrasonic waves (9, 19) thus generated are applied to the workpiece (5). The invention furthermore relates to a workpiece testing system suitable therefor.