The effects of streamer tags and initial prawn size on survival and growth in 2-month- and 7-month-old pond-reared juveniles of Penaeus monodon Fabricius (11-30 mm carapace length, CL) were assessed under laboratory conditions. Tagging did not cause immediate mortality in juveniles of 11-21 mm CL within a one-week period but led to a significantly lower survival rate after 6 to 8 weeks in 1-m³ tanks. However, tagged prawns of 21-30 mm CL showed high long-term survival rates up to 90% in a 12-m³ tank. The 2-month-old juveniles had lower survival rates than 7-month-old prawns. Specific growth rate was not affected by tagging but was significantly higher in smaller prawns. In general, there was no interaction between the effects of tagging and prawn size in terms of growth and survival rates. The lower long-term survival rate associated with tags may be due to the attractiveness of tags to predators, or to trauma or stress caused by the weight of the tags. These factors are discussed in relation to findings for other penaeid species.