Botulinum toxin (BoNT) has become a revolutionary treatment for many neurological, autonomic, gastrointestinal, genitourinary, and cosmetic disorders. The use of this treatment requires expertise in dosage calculations and application technique to avoid potential side effects. Most adverse events (AEs) related to BoNT are local and related to its mechanism of action, i.e., paralysis of unwanted muscles. However, systemic AEs may also be observed. Flu-like symptoms (FLS) are well recognized AEs in patients treated with BoNT; however there is a paucity of information regarding the frequency, clinical impact, and associated risk factors of this particular complication.