Links are to the Castilian versions: if your Catalan is better, there's a language switcher in the top-right.
Who is insured by CatSalut?:
The body which recognises and accredits the condition of insured person is the National Institute of Social Security (INSS).
So if you're registered for social security, you're probably eligible. Take your SS certificate, padrón certificate, and any other document you have to your local health centre.
Access to public health assistance under CatSalut for people who aren't insured or beneficiaries of the National Health System.
The cases listed are:
- Spanish citizens and foreigners who are legal residents in different situations
- Poor foreigners who are registered as living in Cataluña but not legal residents
- Recently arrived poor foreigners who are registered as living in Cataluña but not legal residents
- Special cases
- Spaniards and foreigners who are legal residents and have income above 100,000€ p.a.
Basically for the cases which are likely to be relevant to you it boils down to being empadronado and registered for social security.