BACKGROUND: Pain from the musculoskeletal system often occurs in more than one site. This appears to affect prognosis negatively. Knowledge about specific pain patterns is lacking. OBJECTIVES: To define specific patterns of musculoskeletal co-complaints occurring alongside a primary musculoskeletal complaint. METHODS: Using data from an interview-based health survey of a nationally representative sample of the adult Danish population in 1991 (n = 4817), we describe the co-occurrence of musculoskeletal complaints. Using latent class analysis, we identify clusters of musculoskeletal complaints. RESULTS: Forty percent reported a complaint during a 2-week period; the most common being the low back, neck, shoulder, and knee, and 40% reported more than one complaint. Two latent classes were found for each of the nine primary pain sites except for the low back where three were found. For all primary pain areas, the largest class had site-specific pain only, whereas the smallest class had diffuse pain covering large parts of the body. For participants with a primary musculoskeletal complaint in the spine, the highest probabilities for co-complaints were at other sites in the spine. For primary complaints in the extremities, co-complaints occurred most commonly at adjacent areas. One noticeable exception was a primary complaint of knee pain where co-complaints were found in more remote areas as the neck and low back. CONCLUSIONS: Unique clusters of musculoskeletal co-complaints can be determined based on primary pain site. These patterns are different for persons with a primary complaint in the spine compared with persons with a primary complaint in the extremities.