Slightly crooked mouth is not a precursor of any disease, but it may be an early manifestation of facial nerve paralysis, cerebral hemorrhage, brain tumor and other diseases. 1. Facial nerve paralysis: this disease refers to facial muscle paralysis caused by damage to the facial nerve, which is related to trauma, infection and other factors, with clinical manifestations such as unilateral facial paralysis, speech leakage, salivation, and crooked corners of the mouth on the diseased side. Slightly crooked mouth may appear in the early stage of the disease. 2. Cerebral hemorrhage: slight mouth distortion may also be the precursor of cerebral hemorrhage. This disease refers to a primary non-traumatic hemorrhage of the brain parenchyma, which is usually associated with hypertension combined with fine and small arteriosclerosis, and other causes include cerebral arteriovenous malformations and blood diseases. Early clinical manifestations include dizziness, headache, limb weakness, etc. When the condition worsens, there will be difficulty in speaking and understanding, numbness of the face and limbs and other symptoms. 3. Brain tumor: this disease refers to a kind of tumor or brain metastasis originated from intracranial tissue. Brain tumor will cause direct stimulation, destruction and compression to brain nerves, which will lead to symptoms of neurological deficits, such as headache, vomiting, mental disorder, abnormal language function and so on. At the beginning of the disease, there may be a slight crookedness of the mouth. It is important to pay attention to the symptoms of a mildly crooked mouth and seek medical attention to identify the cause in time to prevent the disease from developing into a serious one.