We describe the initial results of a programme to detect and identify extended X-ray sources found serendipitously in XMM-Newton observations .
We have analysed 186 EPIC-PN images at high galactic latitude with a limiting flux of 1 \times 10 ^ { -14 } erg cm ^ { -2 } s ^ { -1 } and found 62 cluster candidates .
Thanks to the enhanced sensitivity of the XMM-Newton telescopes , the new clusters found in this pilot study are on the average fainter , more compact , and more distant than those found in previous X-ray surveys .
At our survey limit the surface density of clusters is about 5 deg ^ { -2 } .
We also present the first results of an optical follow-up programme aiming at the redshift measurement of a large sample of clusters .
The results of this pilot study give a first glimpse on the potential of serendipitous cluster science with XMM-Newton based on real data .
The largest , yet to be fulfilled promise is the identification of a large number of high-redshift clusters for cosmological studies up to z = 1 or 1.5 .