Within the cathedral, the former sacristy has been converted into a small museum (schatkamer) containing historical artefacts from Haarlem's Catholic past.

Only 19 years later, after the Siege of Haarlem, the church was confiscated and converted to Protestantism as part of the Protestant Reformation.

[2] At this time most of the art and silver artefacts were also seized and what has survived is now in the collection of the Frans Hals Museum.

There are old chasubles, dalmatics, and surplices of the Haarlem clergy, richly embroidered, and showing popular Catholic themes.

The French ones are probably also from the Louis Napoleon period, but the earliest are Flemish in origin and date back to the early 16th century.