This publication contains summary tables of the official statistics for calendar year 1990 on the occurrence of notifiable diseases in the United States. This information is solicited and compiled through entries to the National Notifiable Diseases Surveillance System (NNDSS). In this year's publication, an additional section of information has been added. This section is a bibliography that identifies references for most notifiable diseases. Subject matter experts for each disease were consulted, and these experts identified up to three references they believed to be most useful or informative. Part I contains information on morbidity for each of the 49 currently notifiable conditions. The tables show the number of cases of notifiable diseases reported to the Centers for Disease Control (CDC) for 1990, as well as the distribution of cases by month, geographic location, patient's age, and race/ethnicity. Part II contains graphs and maps depicting summary data for many of the notifiable conditions described in tabular form in Part I. Part III includes tables showing the number of notifiable diseases reported to CDC and to the National Office of Vital Statistics for the past 50 years. It also has a table of deaths associated with specified notifiable diseases reported to the National Center for Health Statistics, CDC, for the period 1979-1988.