The Lassale was Seiko’s ultra thin, high end line of the 1980’s, and this would not have been a cheap watch.  Model reference 9900-5429.


From the serial number on the case back we can accurately date this watch to being made in February 1982.


Jean Lassale were a company that rocked the watch industry.  Founded in 1976, they released the thinnest mechanical watch movement at just 1.2mm, and won many awards.  Technical brilliance doesn’t guarantee commercial success though, and by 1979 they were in financial trouble.  The brand was bought by Seiko, and the ultra thin movements and patents were bought by Piaget (and later Vacheron Constantin also used their movements – not bad from a short lived start up!).  So while Seiko had the well respected brand they used their own ultra thin movements with the Lassale name, and this is a fine example.  At just 4.1mm thin including the case it is well under the 5mm ultrathin classification.  The bi metal rectangular case is absolutely right for the time too.  We will install a brand new battery before sending the watch out to the new owner.  The leather strap is nearly new, and could be swapped for a different colour if preferred.  We kept this Jean Renat strap on the watch as it too is very thin, so suits rather well

This watch will be supplied with our branded presentation box and our Certificate of Authenticity.

Please see the HD video for more detail.  All photos and videos are part of the description and are of the actual watch unless mentioned.  We do not photoshop any pictures, and the images are copyright of and should not be used without permission.


Width with crown  27.7 mm

Width without crown  26.5 mm

Between lugs  18 mm

Lug to lug length  33.7 mm

Case Thickness  4.1 mm

All sizes are approximate.  The watch is photographed on a wrist of 190mm/7.5 inches.

Included with this watch is a 3 month guarantee and free delivery to UK addresses.  If you live outside the UK we can still deliver to most countries.  Please see our Worldwide Shipping information, or Contact Us.   Payment can be made by most credit or debit cards, bank transfer or PayPal.

From 1st September 2021 we will be planting a tree for every watch we sell, working with the International Tree Foundation (Est 1922) to make this business positive on carbon.  By buying anything pre owned you are effectively reusing what already exists, but this takes it further and makes us feel good.