The five types of problems discussed are definitions of maltreatment, the source of study population, the source of comparison groups, subject recruitment, and subject retention in longitudinal research. Explicit definitions of maltreatment are critical in determining whether various types of maltreatment have different causes, correlates, or consequences. Different types of maltreatment should be assessed separately. Study samples should be as representative as possible of the populations from which they are drawn. The choice of study populations should reflect study goals. Comparison groups of nonmaltreated children are necessary to determine whether the effects of maltreatment are independent of other factors known to influence child development. These groups should be similar in life experiences and circumstances to the maltreated groups. Since subject recruitment may prove difficult, considerable attention must be given to methods for increasing response rates. Maintaining study samples over time requires diligence and perseverance. Decisions about the length of time between assessments in longitudinal studies must take into account the likelihood of relatively poor retention rates. Sample sizes must be large enough to withstand the loss of subjects over time. Access to appropriate populations may require the cooperation of various agencies, such as protective service agencies or hospitals. Thus, research objectives must fit overall agency goals, and findings must be useful for policy and program development. 21 references