If you are a male, 18-25 years old, you must register!
The law states that you need to register within 30 days of your 18th birthday. Registration with Selective Service is also required for various federal programs and benefits, including the Free Application for Federal Student Aid (FAFSA), student loans and Pell Grants, job training, federal employment and naturalization.
Please visit their site to register or check if you already registered.