Interesting

Joe Employee as your direct supervisor, it is my job to help you be as productive and effective as possible. Well there is an issue that we need to discuss and get the situation fixed so you can be successful in your current job situation. There appears to be a body odor situation in your life right now. Are there any explanations for this. Washing machine broken down? Change of eating habits? Medical? Stress? What can I do to help you?

Personally, I believe that THE most important consideration is "how" you handle the situation and, in particular, how you speak to them during the talk that you definitely should have with the person.
Most importantly, be certain that this chat is held in absolute privacy ... it could prove to be tremendously embarrassing to the person if others overheard the discussion. Refer to the situation as a "personal hygiene" concern rather than body odor, which carries a definite negative connotation.
Surveys conducted overwhelmingly indicate that if a person has body odor or bad breath, that person wants to be told about it. They want to hear it from a friend rather than an acquaintance or a fellow office worker or a boss, if at all possible, so the key is for the friend to talk to the person privately, perhaps starting by saying if the roles were reversed he/she would hope the person would say something to them. Keep things positive, and remember that this will most likely come as a surprise to the individual—they will most likely be sensitive about the topic, though hopefully thankful that you've brought it to their attention.
Keep in mind that there may be a medical condition, or a medication taken for a medical problem, that is causing the odor. Whatever the cause of the odor problem, you have to address it and be as straightforward, considerate and non-threatening as possible ... be sure to approach the talk with tact and discretion. Talk to this person the way you would want someone to speak to you if you were the one with the personal hygiene concern.

We recently experienced this situation, not because of the warm weather, but due to an incontinence issue that was ignored and not handled properly. Lillian is very right, the 'how' and addressing the issue as delicately as possible is just as important as addressing it so that other co-workers and productivity don't suffer. Being direct and giving specific examples while respecting the person's dignity is the key to getting the issue recognized, acknowledged and corrected by the employee. If the employee does not accept responsibility that a problem exists and/or does not offer a reason for the issue, repeat the example(s) and indicate that others have noticed the lack of hygiene/hygiene issue and the situation needs to be corrected immediately. It is good to follow the conversation with an email that the employee can acknowledge receipt of. If the situation does not correct itself, then it must proceed through your company's disciplinary process and having an acknowledgement of a conversation will help with initiating the process if necessary. Again, I agree to refer to the situation as a hygiene concern and not body order. Good luck.

I've never heard of this approach, yet, I must say that I like it. Why? It delicately yet directly places ownership with the employee while letting him/her know that his office "family" cares and wants things "normal" again. And to your point, we are speaking of adults hygeine versus that of a mid- or high-schooler, which would likely take a more "help me understand" approach.

Okay Guys, Well today is "the" day. I have an emplooyee that has a major body odor. You can smell him throughout the office. This has been going on since May, it's now September. This is not attributed to a medical condition. He is going through a divorce and does not take care of himself as he once did. This morning I had two employees come in a complain. So I must speak with him. Wish me luck!