You should definitely add the German abbreviation (if not 'Bankleitzahl') to clarify that you're referring to the German sorting code (as opposed to the UK one, for example).

In the UK we talk about
branch sort code
or
branch sortcode

The following links show examples from two banks.
I agree with Ralf that you should include BLZ.

Folks, it has all been standardized and better men (in banking circles it is mostly men) have racked their brains to come up with BIC. See the reference below; it is so exhaustive it made my poor li'l head spin.

This is what we call it in the States.
I always translate it this way. I have done so for years and have hear nary a murmur.

20 years a translator + 20 yrs a lawyer

Of course the German is Bankleitzahl.

I don't know if you are asking because you have received an invoice from someone in Germany of if you are a translator.

If you have to translate the term, we might be getting ourselves into trouble by trying to be too specific. Looking at Didi's reference, we can see that the BIC is not the same as the BLZ. It will probably lead you to the same bank but it is not the same number.

http://www.zahlungsverkehrsfragen.de/frameset.html

"Jeder SWIFT-Teilnehmer hat eine eindeutige Kennung, den sogenannten BIC (Bank Identifier Code). Dieser hat 8 oder 11 Stellen und ist wie folgt aufgebaut:

bank code
4 Stellen Alphazeichen frei gewählt (Bundesbank z.B. MARK)

country code
2 Stellen Alphazeichen, ISO-Code des Landes (in Deutschland also DE)
location code

2 Stellen alphanumerisch zur Ortsangabe (z.B. FF für Frankfurt)
branch code

wahlweise 3 Stellen alphanumerisch zur Bezeichnung von Filialen"

Another part of the problem is the number of different English names for BLZ, such as "routing code", "transit number", "bank code (number)", "bank identification number", "bank number", "sorting code", "routing symbol", all coming up somewhere in Hamblock/Wessels – Großwörterbuch Wirtschaftsenglisch, Zahn – Wörterbuch Bank- und Börsenwesen, Reinhart von Eichborn – Der kleine Eichborn, and Romain – Wörterbuch der Rechts- und Wirtschaftssprache.

If you are sure your translation will only be read in only one English language country, a Google search with "Bankleitzahl" in the domain for that country might give you the correct translation for that country's readers. For example, this site indicated that the New Zealand translation might be "sort-code" or "sort code" as shown at this .nz domain site:

http://www.google.com/search?q=cache:RWxXpKvrVxA:www.anthrop...

The exact term "sort-code" did not turn up in any dictionary and the above text originated in Switzerland. A further search for "sort code" and .nz did however yield some authoritative hits indicating that the term in New Zealand may indeed be "sort code". Similar detective work might give you exactly the right term for your readership.

Otherwise, a more general and explanatory translation, such as "German Bank Code (Number)" or similar might be less dangerous than arbitrarily picking one of the above terms.

HTH

Dan