  Open clusters belonging to star-forming complexes are the leftovers from the
initial stellar generations. The study of these young systems provides
constraints to models of star formation and evolution as well as to the
properties of the Galactic disc. We aimed at investigating NGC1981, a young
open cluster in the Orion Nebula Region, using near-IR and BV (RI)C photometric
data.We devised a method that accounts for the field contamination and allows
to derive photometric membership for the cluster stars. A new cluster centre
was determined by Gaussian fittings to the 2-D stellar distribution on the sky,
and has been used used to obtain the radial stellar density profile and the
structural parameters. Mass functions were computed for stars inside the
cluster limiting radius and total mass estimated from them. Although more
easily distinguished by its grouping of 6 relatively bright stars, an
underlying population of faint pre-main sequence stars is evident in the
cluster area. We showed that this population is related to the cluster itself
rather than to the nearby Orion Nebula cluster. Additionally a fraction of the
cluster low mass stars may have been evaporated from the region in its early
evolution leading to the present sparse, loose structure. The estimated
parameters of NGC1981 are core radius Rc = 0.09 +/- 0.04 pc, limiting radius
Rlim = 1.21+/-0.11 pc, age t = 5+/-1 Myr, distance modulus (m-M)0 = 7.9+/-0.1
(380 +/- 17 pc), reddening E(B - V)= 0.07 +/- 0.03 and total mass m = 137 +/-
14 M\cdot.
