This study examines herd behaviour in four Southeast Asian stock markets, namely Indonesia, the Philippines, Malaysia, and Vietnam. Empirical results indicate that except for the Philippines, herding exists in the other three markets. Stronger evidence of herding has been detected in these markets when the market is up. When the market is down, it is only the Malaysian market that exhibits signifi cant herding. The study further investigates herding by dividing the entire sample period into two sub-periods: pre-crisis and during economic crisis. We fi nd strong evidence of the existence of herding in Indonesia and Malaysia in both sub-periods. However, the fi ndings are mixed when we additionally examine herding in up and down market scenarios during the two sub-periods by using modifi ed models.