OBJECTIVE: To investigate the relationships between sagittal alignment parameters and Neck Disability Index (NDI) scores after adjacent 2-level anterior cervical diskectomy and fusion (ACDF) and to study the impact of the T1 slope (T1s) minus C2-7 lordosis (T1s-CL). METHODS: In total, 76 patients after adjacent 2-level ACDF were retrospectively analyzed. Radiographic measurements included T1s, C2-7 lordosis, T1s-CL, segment angle (SA), and C2-7 sagittal vertical axis (SVA). NDI scores were used to evaluate clinical prognosis. Pearson correlation coefficient was calculated between radiographic measures. Linear regression analysis was used to analyze the relationships between follow-up cervical sagittal parameters and NDI. RESULTS: ΔT1s was positively correlated with ΔC2-7 lordosis (r = 0.466, P < 0.001), ΔT1s-CL (r = 0.337, P = 0.003), ΔC2-7 SVA (r = 0.238, P < 0.05), and ΔSA (r = 0.654, P < 0.001). ΔC2-7 lordosis was positively correlated with ΔSA (r = 0.692, P < 0.001) and negatively correlated with ΔT1s-CL (r = -0.676, P < 0.001) and ΔC2-7 SVA (r = -0.418, P < 0.001). ΔT1s-CL was positively correlated with ΔC2-7 SVA (r = 0.644, P < 0.001). The pre- and postoperative SAs were significantly different (P < 0.05), increasing from 3.71° ± 8.92° to 9.63 ± 4.20°. Preoperative NDI was positively correlated with preoperative C2-7 SVA (r = 0.325, P = 0.004) and T1s-CL (r = 0.498, P < 0.001). Follow-up NDI was positively correlated with follow-up T1s (r = 0.359, P = 0.001), C2-7 SVA (r = 0.613, P < 0.001), and T1s-CL (r = 0.696, P < 0.001) and negatively correlated with C2-7 lordosis (r = -0.491, P < 0.001). The linear regression model showed that when preoperative T1s-CL was greater than 21.43°, the NDI score was greater than 25 (R = 0.248, P < 0.001), and when follow-up T1s-CL was greater than 28.07°, the NDI score was greater than 25 (R = 0.484, P < 0.001). CONCLUSIONS: Changes in cervical sagittal parameters after 2-level ACDF were associated with quality of life. A greater T1S-CL mismatch was related to a greater degree of cervical malalignment. T1s-CL may be a more important predictor of cervical malalignment than C2-7 SVA. Specifically, a mismatch greater than 28.07 corresponded to positive cervical sagittal malalignment, defined as an NDI score greater than 25.