Because of its hydrophobicity and persistence, dichlorodiphenyltrichloroethane (DDT) is ubiquitous in sediments and poses significant risk to benthic organisms. Therefore, it is imperative to evaluate the long‐term toxicity of DDT. However, limited information is available on its chronic toxicity to benthic invertebrates. Full–life cycle toxicity of sediment‐bound DDT to Chironomus dilutus was assessed. Median lethal concentrations (with 95% confidence limits) of DDT and its degradation products (DDX) to C. dilutus were 334 (165–568), 21.4 (11.2–34.3), and 7.50 (4.61–10.6) nmol/g organic carbon after 10‐, 20‐, and 63‐d exposure, respectively. In addition, median effect concentrations of DDX were 20.0 (15.0–25.3), 7.13 (4.10–10.5), and 8.92 (3.32–15.1) nmol/g organic carbon for growth, emergence, and reproduction, respectively. A toxicity spectrum was established to visually summarize chronic effects of DDX to midges. In addition, DDT degraded to dichlorodiphenyldichloroethane (DDD) and dichlorodiphenyldichloroethylene (DDE) during sediment aging, and their toxicity differed from that of the parent compound. Predicted toxic units of DDX in porewater were utilized to distinguish between toxicity from DDT and that of DDD and DDE. The results showed that DDD was the main contributor to the toxicity in C. dilutus. To improve the accuracy of sediment risk assessment of DDT, the composition of DDX should be considered. Environ Toxicol Chem 2019;38:2698–2707. © 2019 SETAC