We study the long-term light and spectral variations in the He-strong magnetic chemically peculiar star HD 37776 ( V901 Ori ) to search for changes of its 1.5387 d period in 1976–2007 .
We analyze all published photometric observations and spectrophotometry in the He i 4026 Å-line .
The data were supplemented with 506 new ( U ) VB observations obtained during the last 2 observing seasons , 66 estimates of He i equivalent widths on 23 CFHT spectrograms and 69 on Zeeman spectrograms from the 6-m telescope .
All the 1895 particular observations have been processed simultaneously .

We confirm the previously suspected increase of the period in HD 37776 which is a record-breaking among CP stars .
The mean rate of the period increase during the last 31 years is 0.541 \pm 0.020 s per year .
We interpret this ongoing period increase as the slowing down of the star ’ s surface rotation due to momentum loss through events and processes in its magnetosphere .