There is a lot to be said about shareholder vs. partner as a translation for Gesellschafter, for a more detailed overview of this discussion, see glossary link below.

I'm becoming increasingly convinced that shareholder is the better translation. The argument brought forward in support of partner is that the GmbH context usually refers to smaller companies, which would have partners, whereas shareholders are found in bigger organsations such as Aktiengesellschaften. I don't consider this persuasive, as the actual size of the company is not the decisive factor and the relevant legislation does not base its definitions on size. In addition, the size argument is not even based on the factual situation, as GmbHs can be of considerable size; in fact, they can be so large as to require the formation of an Aufsichtsrat.

To back up my answer, here a few examples from the UK, with "Limited" standing for public limited company, the closest British equivalent of a GmbH (btw: stockholder is a US term):

An international investor on the financial markets who has provided seed capital to a number of private businesses as well as previously being a strategic investor in a number of public companies. Joe is the ***sole shareholder*** of Sweetland Limited, which is a major shareholder in Paradigm.

Pamela has worked at Elton for over 12 years primarily in a sales capacity. She became a shareholder in 1998 and was instrumental in managing a smooth transition when the founder of the Company retired in April 2000. At this time Pamela became the ***sole shareholder*** of the Company. (Note: this company is a plc)
http://www.eltongames.com/management.htm

I'll leave it at that, but if you google for "sole shareholder + plc", you'll get a good overview of the standard usage in GB.

--------------------------------------------------
Note added at 2002-11-17 10:01:41 (GMT)
--------------------------------------------------

And here s.th. for Bougie\'s edification: \"limited by liability\" is simply a translation of the German \"mit beschränkter Haftung\". Two forms of private limited companies exist in the UK, private companies limited by shares (the most common form and in its structure and liability requirements closest to a GmbH), and private companies limited by guarantee (Gesellschaft mit beschränkter Nachschusspflicht) ... there you go.