Disassembly for recycling purposes is an emerging area of research that offers many advantages over more traditional means of recycling. However, many technical challenges are involved in automated disassembly. This paper addresses one of the critical challenges involved: diagnostics in the unscrewing operation. The various conditions that can arise when one attempts to unscrew a screw (one of which is the successful removal of the screw) are categorized, and a diagnostic procedure for detecting which condition has occurred and deciding what subsequent action to take is developed. Experimental condition detection results are presented.