Accompanying leg pain is commonly observed in patients with chronic low back pain (CLBP) and is assumed to be an indicator for the disorder severity. However, it is still unknown whether it is possible to estimate a patient's functional status by the extent of leg pain present. In a post rehabilitation cohort of 132 patients with CLBP (mean age 44.3 years) the relationship between pain extent and functional status was determined using pain drawings scored for pain extent by a simplified scoring system (Lower Extremity Region: LER) and several function related questionnaires. Primary outcomes were pain extent, pain intensity ratings (Visual Analog Scale: VAS), disability status (Oswestry Disability Index: ODI) and physical and mental health (Short Format 12: SF-12). Statistically significant differences between patients with low (1-2) and high (>= 3) LER scores were found in VAS, ODI and SF-12 physical health scores, however, the LER score has a poor diagnostic accuracy in predicting desirable versus undesirable VAS, ODI and SF-12 scores. Pain intensity (VAS), back disability (ODI) and physical health are worse in CLBP patients with high LER scores. However LER scores cannot be used to predict elevated VAS, ODI and SF-12 scores in an individual patient.