There is little information on the effect of nonsurgical factors or postoperative anemia on achieving spinal fusion. In a prospective cohort study of 184 consecutive lumbar spinal fusions, we obtained data on socioeconomic, clinical, radiologic, and traditional surgical factors and analyzed associations between these factors and fusion status at 6 months post surgery. The overall fusion rate was 74%. Among the surgical factors, use of pedicle screw fixation (p = 0.005) predicted fusion success; postoperative anemia (hematocrit < 30%; p = 0.003) and a history of smoking (p = 0.050) predicted fusion failure. However, when the surgical factors were analyzed together with clinical and socioeconomic factors, back pain greater than or equal to leg pain (p < 0.001) and patients working at the initial visit (p = 0.001) predicted fusion success; shoulder pain at the initial visit (p < 0.001) and a family history of back surgery (p = 0.006) predicted fusion failure. These factors were stronger predictors of fusion status than were traditional surgical factors.