Tobacco, when smoked, negatively impacts most of the body's systems: 

Cardiovascular: heart attack, stroke, atherosclerosis, narrowing of the blood vessels, peripheral vascular disease. It interferes with the efficacy of several medications used to treat coronary heart disease.

Respiratory: It causes 83% of chronic obstructive pulmonary diseases (COPD) including emphysema, chronic asthma, and chronic bronchitis.

Cancer: Includes not only lung cancer, but cancer of the larynx, mouth, esophagus, kidney, bladder, stomach, pancreas, and possibly cervix.
It is Addictive: Everett Koop, from the Surgeon General's office, stated that nicotine is more addictive than crack cocaine.

It is Hazardous to unborn babies. Pregnant women who smoke typically deliver babies that are usually smaller, not as healthy and tend to have more difficulty learning during early school years. 

Passive Smoke has been classified as a Class A carcinogen (cancer causing substance). There are 3,000 nonsmokers annually who die of lung cancer from passive smoke and over 50,000 have related cardiovascular effects. Infants and young children living in a home with a smoker are more prone to inner ear infections, pneumonias, and asthma attacks. 

Other: Cigarette smoke causes cataracts, attributes to poor wound healing, back pain, problems with claudication, and sleep apnea.