Apple Inc. (Nasdaq: AAPL) CEO Steve Jobs announced he is taking a medical leave. Unlike the two previous times he did so, in 2004 and 2009, Jobs notably did not provide a timeline for his expected return.

Having said that, it is still an interesting exercise to look at what happened to the company's stock price during the previous two medical leaves.

The following information are provided by Robert W. Baird & Co.

In 2004, Apple stock declined 2.4 percent on August 2, the day of the announcement. It bottomed out on August 6, having declined 7.9 percent from the time of the announcement.

In 2009, shares dropped 2.7 percent on January 14, the day of the announcement. By January 20, Apple stock had fallen 10.8 percent before bottoming.

Baird pointed out that Apple shares actually started falling since June 2008 on rumors regarding Jobs' health. Using June 2008 as a reference, Apple lost 60 percent through mid January 2009, although that's roughly in line with the performance of broad stock market.

However, from the time Jobs was gone in mid-January 2009 until he returned six months later, Apple stock jumped 60 percent versus the 23 percent gain of the NASDAQ Composite index.

On January 18 2011, the first day the market was open since Jobs' announcement, Apple shares fell 3.50 percent in morning trading.