Maurice,
The question of "priviledge" is a complex one and dependent, not only upon the profession involved, but upon the juridiction the answer concerns. Different states have different rules, but let me see if I can simplify at least some of it for you.

As an attorney, I am bound by attorney - client priviledge regarding any communications I have with my client, including an admission that they had committed a crime. The rationale for this is that an attorney could not adequately defend their client if the things said between them could be used against the client in court. There are only two exceptions to this rule. First, client statements can be disclosed if the attorney needes to defend himself or herself from legal action taken by the client based upon the matter concerning which the information was disclosed (e.g.: in a legal malpractice suit). Secondly, An attorney may break priviledge where the client admits that they are going to commit a crime in the future, and/or to protect another person from harm. With those exceptions, the courts generally accept this priviledge as absolute.

The priviledge between a physician and a patient is similar, but not as absolute. Medical records can be obtained via a subpoena where applicable, and there are instances where courts have rejected the claim of priviledge based upon specific facts of a case, but generally a physician is permitted to maintain priviledge in a similar manner to an attorney, and for similar reasons. This is especially true where the information being sought is medical in nature, rather than a "confession" to a crime. Moreover, where someone is serving a dual role (i.e. physician and attorney), the type of privledge would depend upon which role the individual is filling at the time.

There is a more interesting issue regarding priviledge and confidentiality for physicians, however. Suppose a physician has two patients who are related somehow (e.g. a husband and an ex-wife) and he is treating both as patients. Now, suppose the physician discovers, during the course of treating one of them, that they have a communicable disease (e.g. HIV). Finally, suppose the husband has continued to have unprotected sexual relations with his ex wife, but asks the physician not to discose his diagnosis to her; keep it confidential. The problem here, is that the physician has a duty to both patients, and he or she has to choose one or the other. In essence. the physician is damed if they do, and damed if they don't. I know what I did in this situation, but I'd love to hear your readers' comments first.

As always another thoughtful question and an excellent answer from Dr. Shore. At the risk of sounding like "me too..."

There are several frequently conflated issues here. "Privileged communication" as a legal term of art generally applies to the ability of a court of competent jurisdiction to compel a party to reveal the contents of a conversation without subjecting the contents to hearsay rules or other exclusions. The nature of attorney-client relationships frequently involve some breach of law. Thus compelling the attorney to reveal confidential discussions may immediately compromise the accused's defense or rights.

In contrast, medical care may typically be rendered without revealing criminal activity. A perpetrator may state "I was shot doc." The additional information "I was just robbing a couple little old ladies when one of 'em drew down on me and fired" is interesting (entertaining even) but hardly necessary to provide medical care.

In both the medical and legal venues professionals may be required to report actual plans of future or ongoing criminal activity. This is a public policy issue. It constitutes the basis for mandatory communicable disease reporting, domestic violence, abuse of children and the elderly and to some extent "Tarasoff rules." These are less issues of professional privilege than an governmental determination that public safety (or in the case of Tarasoff safety of an identifiable individual) trumps a right to privilege or privacy.

It's important to note that some jurisdictions don't have either Tarasoff-like rules or mandatory reporting of some medical conditions.