Objective. Research on chronic low back pain (cLBP) has focused heavily on structural abnormalities with emphasis on diagnostic imaging. However, for many cLBP patients, clinical pain and disability are not clearly associated with identifiable pathology of the spine or associated tissues. Therefore, alternative determinants such as psychological factors and dysfunctional pain modulatory processes have been suggested to be important. Methods. This observational study examined differences in pain catastrophizing and endogenous pain modulation between 25 cLBP patients and 25 pain-free controls. Associations among pain catastrophizing, endogenous pain modulatory processes, clinical pain reports, and disability were also examined in cLBP patients. Endogenous pain modulation was examined using temporal summation (TS) of mechanical and heat pain stimuli as well as conditioned pain modulation (CPM) with algometry (test stimulus) and the cold pressor task (conditioning stimulus). Results. Findings demonstrated significantly greater pain catastrophizing as well as greater TS of mechanical and heat pain for cLBP patients compared with controls. CPM was not present in cLBP patients or controls. Among cLBP patients, pain catastrophizing was significantly associated with disability, while TS of mechanical pain was significantly associated with clinical pain severity and disability. Conclusions. This study suggests that endogenous pain modulatory processes are altered for cLBP patients, particularly TS of mechanical and heat stimuli. Pain catastrophizing and TS of mechanical pain may have important clinical relevance for cLBP, given associations with clinical pain and disability; however, future research is needed to replicate these findings.