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It is commonly assumed that, for a variety of conditions, E/Hp(10) conversion coefficient is below unity, i.e., Hp(10) can be used as a conservative surrogate of effective dose. The validity of this assumption was checked by Monte Carlo simulation of E and Hp(10) as determined by a practical dosemeter. The calculations concerned irradiation by parallel photon beams with directions varying within a 4p solid angle and energy ranging from 50 keV to 1 MeV. Observed dependences of conversion coefficients on irradiation geometry, photon energy and dosemeter position demonstrate that in strongly anisotropic radiation fields straightforward application of Hp(10) for assessment of effective dose may lead to significant underestimation of the latter. For photon energy of 80 keV this underestimation may be up to 16-fold. For simulation of real life situations, irradiation by photons coming within broad cones (with solid angle p) was considered. It was found that even for this irradiation geometry, E/Hp(10) may be as high as 4.3. At the same time, for radiation coming from the frontal hemisphere, the values of conversion coefficient for a typically positioned (i.e., the left chest pocket) personal dosemeter do not exceed unity. The conclusion was reached that prior to application of Hp(10) as a surrogate of effective dose, the information regarding angular distribution of radiation fields must be taken into account.