STUDY DESIGN: Narrative review and discussion of the selected literature. OBJECTIVES: To discuss some important methodologic challenges in low back pain research in primary care. SUMMARY OF BACKGROUND DATA: Many methodologic problems must be confronted when conducting low back pain research. Some of these problems are back pain specific or specific to the primary care setting. METHODS: Methodologic problems related to four research issues will be discussed: study designs, definition of low back pain, determinants of low back pain, and outcome assessment. RESULTS: Two fundamentally different study designs are frequently used in low back pain research, namely observational studies and experimental studies. The definition of low back pain is typically restricted to a highly variables self-reported symptom, the sensation of pain in the back. There clearly is a need for an evidence-based classification system for low back pain. Because a tenable theoretical framework is lacking, it is difficult to know which determinants of low back pain should be quantified. Low back pain studies focus usually on health-related quality-of-life outcome parameters. The identification of the minimum clinically relevant changes for the most important outcome instruments needs further consideration. CONCLUSIONS: In years to come, low back pain researchers are challenged to overcome some of these (and other) problems to enhance the quality of low back pain research in primary care.