Objectives To evaluate the impact of preoperative frailty on short-term outcomes following complex head and neck surgeries (HNSs). Study Design Cross-sectional database analysis. Setting American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database. Methods The 2005 to 2017 ACS-NSQIP was queried for patients undergoing complex HNS. Five-item modified frailty index (mFI) was calculated based on functional status and history of diabetes, chronic obstructive pulmonary disease, congestive heart failure, and chronic hypertension. Results A total of 2786 patients (73.1% male) with a mean age of 62.0 ± 11.6 years were included. Compared to nonfrail patients (41.2%), patients with mFI ≥1 (58.8%) had shorter length of operation ( P = .021), longer length of stay (LOS) ( P < .001), and higher rates of 30-day reoperation ( P = .009), medical complications ( P < .001), discharge to nonhome facility (DNHF) ( P < .001), and mortality ( P = .047). These parameters remained statistically significant when compared across all individual mFI scores (all P < .05). After adjusting for age, sex, race, body mass index, smoking, and American Society of Anesthesiologists score via multivariate logistic regression, patients with mFI ≥1 were significantly more likely to undergo reoperation (odds ratio [OR], 1.39), surgical complications (OR, 1.19), medical complications (OR, 1.55), prolonged LOS (OR, 1.29), and DNHF (OR, 1.56) (all P < .05). Multivariate logistic regression also demonstrated that after adjusting for confounders, compared to patients with mFI = 1, patients with mFI = 2-5 (18.7%) were more likely to undergo shorter operations (OR, 0.74), have medical (OR, 1.46) or any complications (OR, 1.27), and have DNHF (OR, 1.62) (all P < .05). Conclusion The 5-point mFI can independently predict short-term surgical outcomes following complex HNS. This simple and reliable metric can potentially lead to improved preoperative counseling and postoperative planning for complex HNS patients.