This chapter describes the acute upper extremity pain. The upper extremities are common sites for acute pain or chronic pain with acute exacerbations. The most common etiologies of upper extremity pain include trauma, tumor, infection, and neuropathic pain. Successful treatment of acute upper extremity pain usually involves a multifaceted approach utilizing medications, physical therapy (PT), and regional anesthesia depending on the etiology. If the cause of acute pain is not obvious, one needs to be sure to be aware of underlying pathology including stroke, ischemia, and venous thrombosis. Treatment of acute upper extremity pain is usually aided by the use of analgesic medications such as nonsteroidal anti-inflammatory drugs (NSAIDs), acetaminophen, and opioids. A well-colored figure on cutaneous distribution of upper extremity peripheral nerves and a well-illustrated table on blocks for nerves of upper extremities are also presented in this chapter.