From 1 January 1981 to 31 December 1982 information on all births to Bedouin Arab women residing in the Negev Desert of Israel showed a previously unreported seasonal pattern. The peak season, November-February, coincided with the period of cool temperatures and the Bedouin Arab cultural seasons of winter and spring. This pattern is different from those of Jewish and Christian groups in the same region, a difference not attributable to religion alone. Sociodemographic factors associated with the peak season of birth include traditional occupations of fathers, multiparae 2+, and traditional place of residence. This pattern has persisted over the past 15 years although it is less apparent among the more recently sedentarized Bedouin Arabs.