Abstract To perform quality inspection in the injection process is a complex task due to high number of defects that could occur in an injected part and the high number of process parameters that could produce them. Injection defects, in particular qualitative ones, are not a clear reference to determine correct process parameter value setting to produce good quality parts. Research results show that the occurrence of each injection defect could be caused by specific parameters with values above or below an optimal one. Although this information is a guide for the defect correction, the effective correction of qualitative defects with parameter modifications is very complex. This is due to the problems that arise when transforming a qualitative defect into a quantitative inspection. This article shows an inspection model to assist the qualitative defect intensity classification using defect behavior tendency curves. These curves have been deduced from generic analytical relationships established between injection defects and injection process parameters. Conducted tests allow validating the approach and its initial effectiveness. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers