Usual intake estimates describe long-term average intake of food and nutrients and food contaminants. The frequencies of fish and shellfish intake over a 30-day period from National Health and Examination Survey (NHANES 1999-2006) were combined with 24-h dietary recall data from NHANES 2003-2004 using a Monte Carlo procedure to estimate the usual intake of fish and shellfish in this study. Usual intakes were estimated for the US population including children 1 to <11 years, males/females 11 to <16 years, 16 to <21 years, and adults 21+ years. Estimated mean fish intake (consumers only) was highest among children 1 to <2 years and 2 to <3 years, at 0.37 g/kg-day for both age groups, and lowest for females 11 to <16 years, at 0.13 g/kg-day. In all age groups, daily intake estimates were highest for breaded fish, salmon, and mackerel. Among children and teenage consumers, tuna, salmon, and breaded fish were the most frequently consumed fish; shrimp, scallops, and crabs were the most frequently consumed shellfish. The intake estimates from this study better reflect long-term average intake rates and are preferred to assess long-term intake of nutrients and possible exposure to environmental contaminants from fish and shellfish sources than 2-day average estimates.