We sought to assess correlational relationship between mental health and outcomes following lateral lumbar interbody fusion (LLIF). Patients who had undergone LLIF were identified. Patients with indications for surgery including infection, trauma, or malignancy were excluded. Patient-reported outcomes (PROs) included short-form (SF)-12 Mental Component Score (MCS)/Patient Health Questionnaire (PHQ)-9/Patient-Reported Outcomes Measurement Information System−Physical Function (PROMIS-PF)/12-Item Short-Form Physical Component Score (SF-12 PCS)/Visual Analog Scale (VAS) back and leg pain/Oswestry Disability Index (ODI) and were collected preoperatively and at several postoperative time points extending to 1 year. Pearson correlation tests were used to compare the 12-item Short Form Mental Component Score (SF-12 MCS) and PHQ-9 with the other PROs. We included 124 patients. SF-12 MCS positively correlated with PROMIS-PF at 6 months (r = 0.466) and SF-12 PCS preoperatively (r = 0.287) and at 6 months (r = 0.419) (P ≤ 0.041, all). SF-12 MCS negatively correlated with VAS back preoperatively (r = −0.315), at 12 weeks (r = −0.414), and at 6 months (r = −0.746); VAS leg at 12 weeks (r = −0.378); and ODI preoperatively (r = −0.580) (P ≤ 0.023, all). PHQ-9 negatively correlated with PROMIS-PF at all periods except 12 weeks (range: r = −0.357 to −0.566, P ≤ 0.017, all) and SF-12 PCS preoperatively, at 6 weeks, and at 6 months (range: r = −0.363 to −0.562, P ≤ 0.022, all). PHQ-9 positively correlated with VAS back at all periods before 1-year (range: r = 0.415–0.690, P ≤ 0.001, all), VAS leg at 12-weeks (r = 0.467) and 6-months (r = 0.402) (P ≤ 0.028, both), and ODI at all periods except 6-months (range: r = 0.413–0.637, P ≤ 0.008, all). Better mental health scores correlated with superior physical function, pain, and disability scores when measured by both SF-12 MCS and PHQ-9. PHQ-9 more consistently reported significant correlation to all outcomes measured when compared to SF-12 MCS.