Chiropractic adjustments are safe! The risk of any serious injury is unlikely, in fact many chiropractors won't even see one in their office throughout their entire career. Although there are reports of stroke following a cervical adjustment, the likelihood of this happening is minimal. Recent studies show that there is no cause and effect relationship between the two. You are just as likely to suffer a stroke by tipping your head backwards like you do while getting your hair done at the hair salon, gazing at the stars, catching rain drops in your mouth, or painting the ceiling in your bedroom.
Chiropractors are highly trained professionals with hours of practice and training to look for signs that would lead them to believe an adjustment would cause harm to their patient. I am a student of chiropractic at the New York Chiropractic College and we spent an entire trimester alone discussing the risks, signs and symptoms, and "red flags" to look for while we are taking an in depth history. We practice cervical adjustments every day and I personally have witnessed hundreds of them without a single serious complication occurring. I perform them on my friends and family without any concern for such an injury. One thing I've come to understand and practice is I ask myself with every patient I see, "what would I do if this patient were either my mother or father?" We also learn tests to perform on our patients prior to adjusting if we come across a lower ranking concern such as head aches after an upper respiratory tract infection or head aches accompanied with vertigo/dizziness.
There are more cases of death reported following treatment from a medical doctor then there are for chiropractors. It has been noted by many that medical doctors typically do not take back pain patients seriously and do not know how to treat a patient complaining of back pain. They prescribe NSAIDs which with chronic use have been known to cause serious complications more than a chiropractic cervical manipulation. As with every profession, there are chiropractic doctors out there who do not perform the evaluations they are taught in their education prior to treating their patients. This is why it is important to research the doctors in your area before scheduling an appointment as it is with any other medical issue you happen to come across in your life.
Here are some links that provide a little more support: http://www.acatoday.org/content_css.cfm?CID=3134
http://www.acatoday.org/press_css.cfm?CID=2671
http://www.chiro.org/LINKS/stroke.shtml
This link shows the comparison of death rates related to stroke, very interesting! -- http://www.chiro.org/LINKS/CVA/Cerebrovascular_Accidents.shtml#Table_2
I hope this has helped answer your question and provided a little more promise in the chiropractic profession. Please let me know if you have any other questions about this topic or any regarding chiropractic.