Background: In high-intensity, mixed and pulsed neutron fields the use of spectrometers or area monitors with active detectors is useless in these conditions neutron measuring devices must have a passive detector. Here a passive neutron area monitor with CR39 track detector was designed and the response was calculated. Materials and Methods: The response of a passive neutron area monitor with CR39 track detector has been calculated with the MCNPX code. To increase the detection efficiency a 10B converter was included. The response was calculated using 47 monoenergetic neutron sources. Results: A passive neutron area monitor using a CR39 with 10B converter was designed where fluence and H*(10) responses were calculated. Conclusion: The shape of the responses is similar to responses reported for neutron monitors with active detectors.