Most guys see signs of puberty by the time they are 15 years old; if you haven’t noticed any signs of puberty by this age, you should discuss it with your health care provider (HCP). Signs of puberty include growth of dark facial and pubic hair and enlargement of the penis and testicles. These changes are caused by the hormone testosterone. There are many different reasons for puberty to be delayed, including being malnourished (i.e., not eating enough food or not getting enough vitamins and minerals), having certain chronic medical conditions like diabetes, or having problems with the thyroid or pituitary glands (tiny structures in your body that produce hormones). When you talk to your HCP, they may refer you to an endocrinologist (a doctor who specializes in caring for people with hormone or growth problems) who will likely ask you about your general health, any medicines or supplements you are taking, and the pattern of growth of you and your family members (parents, siblings). They may recommend blood tests to check the levels of certain hormones as well as an x-ray of your hand, which can give a sense of how much you have left to grow. The good news is that once your medical providers find out why your puberty has been delayed, in most cases treatment is possible to get puberty started.