Ustekinumab is a monoclonal antibody targeting the p40 subunit of interleukins IL‑12 and IL‑23. It has demonstrated efficacy in mucosal healing and is indicated for moderate to severe Crohn’s disease in adults with poor response to anti‑TNF therapy or contraindications. Common adverse effects include upper respiratory infections, nausea, and dizziness. Although generally well tolerated, rare reactions such as facial paralysis have been reported.A 63‑year‑old male with supraglottic squamous cell carcinoma (cT3 cN2 M0), treated with radical chemoradiotherapy and cisplatin, complicated by severe hematologic toxicity, also had Crohn’s disease managed with ustekinumab. Two days after the first dose, he presented to Primary Care with left facial paraesthesia and deviation of the mouth. Neurological examination revealed left peripheral facial palsy without otalgia, otorrhea, or dysphagia. Differential diagnoses included idiopathic Bell’s palsy, stroke, post‑viral infection, Lyme disease, oncologic toxicity, Ramsay Hunt syndrome, and neoplastic involvement of the facial nerve. Strengths of the case included a thorough neurological assessment in Primary Care, guiding appropriate referral. Limitations were the inability to confirm etiology without imaging. At hospital level, ENT pathology was excluded, and treatment with corticosteroids and ocular protection was initiated. The patient was diagnosed with House‑Brackmann grade IV–V peripheral facial palsy, considered a possible adverse reaction to ustekinumab.The originality lies in the onset of facial paralysis shortly after ustekinumab initiation, a rare adverse effect documented in limited reports. The coexistence of immunomodulatory therapy, oncologic immunosuppression, and acute neurological symptoms required an expanded differential diagnosis.This case highlights the importance of early neurological evaluation and vigilance for rare adverse effects of biologics, especially in immunosuppressed patients. It underscores the need for continuous updating on emerging drug reactions and reinforces the value of coordination between Primary Care and hospital services.The case illustrates the challenges of managing neurological symptoms in immunosuppressed patients with multiple comorbidities, particularly in resource‑limited settings.This case emphasizes the crucial role of the family physician in early detection of neurological signs and comprehensive assessment of complex patients. The possibility of facial paralysis associated with ustekinumab underscores the need for up‑to‑date knowledge regarding biological therapies and vigilant monitoring in Primary Care.