Gastroenteritis: This is the most common cause of vomiting and fever, often due to viral or bacterial infections, leading to inflammation of the stomach and intestines. The symptoms can range from mild to severe and are frequently accompanied by diarrhea.

Food Poisoning: Similar to gastroenteritis, food poisoning can cause vomiting and fever, typically resulting from the consumption of contaminated food. The onset of symptoms can be rapid, and the condition is often self-limiting.
Urinary Tract Infection (UTI): While more common in women, UTIs can cause systemic symptoms including fever and vomiting, especially if the infection ascends to the kidneys (pyelonephritis).
Appendicitis: Although abdominal pain is the hallmark symptom, vomiting and fever can also be present, especially as the condition progresses. It's a surgical emergency if suspected.

Meningitis: Although less common, meningitis is a life-threatening condition that can present with fever, vomiting, and headache. It requires immediate medical attention.
Septicemia: Bacteremia leading to sepsis can cause a wide range of symptoms including fever, vomiting, and can rapidly progress to a life-threatening condition.
Pancreatitis: Acute pancreatitis can cause severe abdominal pain, vomiting, and fever. It's crucial to diagnose and treat promptly to avoid complications.

Brain Tumors: In rare cases, brain tumors can cause increased intracranial pressure leading to symptoms like vomiting and fever, though these are not typical primary presentations.
Addisonian Crisis: A life-threatening condition due to acute adrenal insufficiency, which can present with vomiting, fever, and abdominal pain among other symptoms.
Porphyrias: A group of rare genetic disorders that can cause acute episodes of severe abdominal pain, vomiting, and neurological symptoms, sometimes accompanied by fever.