Postgres - syntax error when trying to add postgis

Question

I'm trying to add postgis to a new database I've just created but I get the following error:

I issue the command in pgadmin:

CREATE EXTENSION postgis

I get error:

ERROR:  syntax error at or near "EXTENSION"
LINE 5: CREATE EXTENSION postgis

This is unusual as I have postgis enabled on the other databases on the same server (using postgressql 9.0)?

* UPDATE * Trying the old way I open psql and issue the following commands but nothing happens:

mydatabase=# -f postgis.sql
mydatabase=# -f postgis_comments.sql
mydatabase=# -f spatial_ref_sys.sql

What I'm I doing wrong.