INTRODUCTION: The Impact Stratification Score (ISS) is a measure of the impact of chronic low back pain (LBP) consisting of nine Patient-Reported Outcomes Measurement Information System (PROMIS-29) items, but no studies have examined the ISS or its association with psychological symptoms in military samples. This study examines longitudinal associations between psychological symptoms and the ISS among military service members. MATERIAL AND METHODS: The study involved secondary data analysis of a sample of active duty U.S. military service members aged 18-50 years with LBP (n = 733). Participants completed the PROMIS-29 at three time points during treatment: baseline (time 1, T1), week 6 of treatment (time 2, T2), and week 12 of treatment (time 3, T3). The impact of LBP was quantified using the ISS (ranging from 8 = least impact to 50 = greatest impact). Psychological symptoms were assessed as PROMIS-29 anxiety and depression scores. Separate autoregressive cross-lagged models examined reciprocal associations of ISSs with anxiety, depression, and emotional distress scores from T1 to T3. RESULTS: Within each time point, the ISS was significantly and positively correlated with anxiety and depression. In autoregressive cross-lagged models, anxiety and depression predicted the ISS at the next time point and associations were similar in magnitude (e.g., anxiety T2 to ISS T3: ß = 0.12, P < .001; depression T2 to ISS T3: ß = 0.12, P <.001). The ISS did not predict future depression or emotional distress scores at any time point, but the ISS at T2 was significantly, positively associated with anxiety scores at T3 (ß = 0.07, P = .04). CONCLUSION: Psychological symptoms consistently and prospectively predict the impact of LBP as measured by the ISS among service members undergoing pain treatment. The ISS may also be associated with future anxiety but not depression. PROMIS-29 anxiety and depression items may be useful adjunctive measures to consider when using the ISS to support LBP treatment planning and monitoring with service members.