One thing you might be wondering when you are thinking about applying to Cambridge is what GCSE grades you need to have a chance of getting in. The first thing to say is that good GCSE grades are an important prerequisite for getting into Cambridge, but they are not usually a deciding factor. A level results are much more important but that does not mean GCSE grades don't matter. If you are thinking about applying to Cambridge, you probably already have GCSEs that are good enough to apply. However Cambridge are very unlikely to use GCSEs as a deciding factor when making admissions decisions.
Now onto what exactly "good" GCSEs are. To be seriously considered when applying, for most subjects you want to have at least about 5 A*s at GCSE, with the rest at mostly A grade level. You can get away with the odd worse grade, for example one B is not going to rule you out. I also know of someone who got into Oxford for physics with 3 A*s at GCSE. However the more A*s you have, the better. Medicine is notoriously difficult to get in for and the AVERAGE student has 8 A*s at GCSE, which means you really cannot have much less than this if you want to do medicine or veterinary medicine. Emmanuel only took 2 people out of 30 who they interviewed in 2006 for veterinary medicine and so the competition for these subjects can be fierce.
The grades I've given here (4/5 A*s for most subjects, 8 A*s for medicine) are really just enough to get your application to be considered. If you only just meet these, you'll need to make you application stand out in other respects. If you want your GCSEs to be a big plus, you'll need to be doing better than the average admitted student.
How high your GCSEs can go will largely be determined by your school. If you go to a comprehensive, you'll be doing well to get 8 A*s but if you go to selective state (grammar) or private school you might well be able to do a lot better. For example I know someone who got in for law with 12 A*s and 2 As at GCSE. However I also know of someone who got rejected with 11 A*s and 2 As at GCSE for economics so GCSEs are not really used as a deciding factor.
If you don't have amazing GCSEs, for example no A*s then Cambridge may ask questions as to why this is but so long as you've got several A*s and As, it doesn't make much difference as to whether you've got 6 A*s or 10 A*s. At this point the decision will probably be made more on other factors, such as the interview and personal statement. Different colleges may also give different weightings to GCSEs.
In summary, so long as you can get several A*s and the rest mainly As, you'll have good enough GCSEs to be seriously considered for a place at Cambridge.
