The 1998 Papua New Guinea tsunami was greater than expected from its earthquake magnitude. The area of significant impact was small, approximately a 30 km stretch near the mouth of Sissano Lagoon, Papua New Guinea. To explain the localized nature of the event, a submarine landslide has been conjectured to be responsible. Our study indicates that offshore bathymetry is critical to predicting tsunami coastal behavior. Model runs with newly obtained bathymetric data indicate that an earthquake fault source combined with the existing seafloor geometry may also explain the concentrated tsunami. Although the definitive cause of the Papua New Guinea tsunami remains uncertain, local bathymetry had a notable effect on the wave behavior. ¿ 1999 American Geophysical Union