The gold standard for correcting cervical degenerative disc disease (CDDD) is anterior cervical discectomy and fusion (ACDF), which is a safe, effective procedure. Horner syndrome (HS) is an extremely rare complication immediately post-ACDF due to impairment of the sympathetic trunk. Herein, we present the case of a 48-year-old woman with CDDD-related pain and radiculopathy who was counselled and consented for C5–6 and C6–7 ACDF. ACDF was performed with standard anterior left-sided incisions at appropriate levels. Unlike our usual practice, deeper-toothed retractors were employed for better exposure. Two cages were inserted at C5–6 and C6–7. The procedural time was standard (180 minutes), without intraoperative complications. The patient experienced significant symptom relief immediately post-ACDF, but developed sudden onset left-sided HS, with ptosis, miosis, and anhidrosis, approximately 48 hours post-ACDF. At a 2-week postoperative follow-up, she exhibited clinical improvement, and by 12 weeks, her HS had completely resolved. To our knowledge, this case is the first documented instance of delayed-onset HS post-ACDF. It may be associated with the type of retractors used, resulting in neuropraxia or strain on the sympathetic chain ganglia. We recommend adequate exposure while minimizing excessive retraction of the longus colli muscle to reduce irritation to the sympathetic trunk.