Black Sabbath and Ozzy Osborne.....  

The band apparently changed their name from Earth to Black Sabbath when they began incorporating occult- and horror-inspired lyrics.

I don't think you need to be particularly worried. Many kids go through a phase of liking what seems to be inappropriate music but it actually seems to do most of them little harm. It's part of growing up and usually a way of 'keeping in' with their peers. The lyrics have less influence, usually, than you might suppose (though if you want to know the lyrics, you can very easily find them on the Internet. Here is just one of many sites (the first that came up in Google when I searched "Black Sabbath lyrics"): http://www.azlyrics.com/b/blacksabbath.html

If you are worried that all he is listening to is Black Sabbath, try to encourage an interest in (and intelligent comparison with) other bands. It's probably best not to try to actively ban him from listening to any band or to express TOO much disapproval of the band or it's lyrics. Your opinion is probably best aired gently and with understanding, or it may be flatly ignored!

No, don't get worried . Sure, they have some pretty racy lyrics, but so does modern Rap/Hip-Hop, & it's probably just a phase he's going through . I personally love Ozzy, although i was never into Black Sabbath . Keep an eye on his behavior, but if it's just him listening to this music, it's cool .

Hi!
I am into Black Sabbath since I was a kid. There's nothing you have to worry about, this is not a sect (anything about religion at all). You have maybe heard about Ozzy and Sabbath's satanic influence and such things but c'mon :) It's just music after all! They started their career during the late 60s. Black Sabbath's music is influenced by The Beatles and the new born psychedelic rock. Yes, you may associate this with drugs and alcohol . . . But I'm a huge Sabbath fan and I've never been interested in drugs . . . Not at all! And, please believe me, I'm sure that 99% of the fans are not into drugs!
What about the scary look? You know, this make-up, long hair and stuff... Hah, it's nothing more than a style. We all want to be different in our own way, isn't it? It's not that bad to look a little scary sometimes :)
You don't have to worry at all!