How do I paint over an old varnished wood ceiling in my bathroom, I want it white.

Have u tried putting GESSO over it? It's white and you can also repaint over the gesso in whatever color you want.

I would suggest sanding it, priming it, and then putting two coats of the white paint of your choice over it. My preference as far as paint products would be Sherwin-Williams and Dutch Boy. Sherwin-Williams owns and makes the Dutch Boy products. In a bathroom, I would use at least a semi-gloss as far as the sheen is concerned.

I was told about a primer (at Lowe's and Home Depot) that is for glossy surfaces. Sorry I don't remember the name of it... but was told most home improvement stores carry it or similar.

For primer I like Kilz they offer ir in oil and latex however for your application I would sand and use two coats of oil based Kilz or equivalent then you can repaint with oil or latex paint I prefer a good Latex semi gloss in the bath areas. If you have anymore questions post back and we will try to help. GOOD LUCK AC

Don't just slap white paint over it without preparation. The former owners of our house did that to all the dark varnished woodwork in order to "brighten" the house. We've been here since 1972 and are still stripping and cleaning up the woodwork (now in the bedrooms). What a pain!!