When diving in Australia there are different regulations & requirements than in other countries. The following rules apply in Queensland:
Introductory or Resort Dives:

You will need to fill in  the Medical Questionnaire given to you by the company you are diving with, & similar to that shown below.  Answering YES to any question will not necessarily disqualify you from diving, but will indicate the need for a medical assessment by a qualified physician prior to diving that conforms to Australian Medical Standard AS4005-1.
Children need to be a minimum of 10 years in age to participate in scuba diving.

Learn To Dive Courses and Referral Programs:

You will need to pass a Dive Medical which has been done in accordance with Australian Standards (AS4005.1) Please be well aware of this and only do a medical outside of Australia if your doctor conducts it in accordance to those exact standards and clearly states it on the top of the medical certificate that he issues. If yours does not state this, there is a very high chance you will have to do another medical in Australia. A dive medical is relatively cheap in Australia

Experienced Divers:

Prior to diving, you may be asked to fill out a Medical Questionnaire; this is not a legal requirement but is done in your own best interest. Some companies make it policy and some don't, unfortunately it is still quite a grey area and the rules are not hard and fast.

The purpose of the questionnaire is to determine whether you should be examined by a doctor. There may be a pre-existing condition that has not stopped you from diving in your own country, but one that  Australian laws do not allow; or perhaps there could be a new condition developed since you became qualified to dive which may well affect your safety while diving now.

So, basically if you answer YES to any of the conditions listed on the Medical Questionnaire (see sample below), we strongly recommend you to see a physician for further assessment. As mentioned above it is far better to visit a physician whilst in Australia, as a valid medical in Australia is one that complies with Australian Standards (AS4005.1).

There have been many cases where a qualified diver has been disqualified from diving when they have already made the trek to the reef, simply because their medical condition becomes known to the dive instructor. At the end of the day the dive instructor is controlling the dives, and your safety is their responsibility whether you like it or not!

Sample Medical Questionnaire

Please note that this is a sample only and may not be same as the questionnaire that you are issued onboard your dive/snorkel trip.

Don't let yourself find out after you reach the reef that you don't qualify medically. Please note that dive medicals are performed by independent doctors, not dive companies, and it is ultimately the decision of the doctor whether to pass you as medically fit to dive. If you are diving in North Queensland, your dive medical must be to Australian Standard 4005.1 (2002) or, due to Government regulation, it will not be accepted.