During 2000, 154 clinical Streptococcus pneumoniae isolates were collected from or through three major hospitals serving the Western, Central, and Eastern regions of the Kingdom of Saudi Arabia. Ninety-one (59.1%) of the 154 isolates were resistant to penicillin with 23 strains (14.9%) highly resistant. Resistance was more prevalent among isolates obtained from patients <10 years of age and from isolates cultured from blood and cerebral spinal fluid. Decreased sensitivity to ceftriaxone, erythromycin, trimethoprim-sulphamethoxazole, and levofloxacin was found in 14.9, 15.6, 9.7, and 1.3% of isolates, respectively. There were no significant differences in the resistance pattern between isolates obtained from patients in the three different geographical areas. Serotypes of 116 isolates revealed the most prevalent types to be (descending order) 4, 3, 19F, 9V, 6A, 19A, 14 and 23F, comprising 75% of all strains typed; 9.5% of isolates were nontypable. S. pneumoniae isolates from Saudi Arabia have become more resistant to penicillin and other antimicrobials over the past 20 years.