We address the question as to whether Ureaplasma urealyticum or Mycoplasma hominis, cultured from the placenta of very-low-birthweight (VLBW) infants, are associated with an increased risk of (a) fetal vasculitis and (b) ultrasonographic cerebral white matter echolucency. The sample consisted of 464 VLBW infants for whom (i) the surface of the chorion was cultured for U. urealyticum and M. hominis; (ii) the placenta was examined histologically; and (iii) a cranial ultrasound scan was obtained close to days 1, 7 or 21. Infants with echolucency were compared with controls in univariable and stratified analyses and in multivariable logistic regressions. Fifty-three per cent of placentas from infants with fetal vasculitis harboured U. urealyticum compared with 18% of controls (P </= 0.001). M. hominis was present in 14% of cases of fetal vasculitis and in 2% of controls (P </= 0.001). Among cases of echolucency, 22% had U. urealyticum compared with 30% of controls (P = 0.33), whereas 17% of these cases and 5% of controls had M. hominis (P = 0.08). Our findings support the hypothesis that U. urealyticum in the placenta of VLBW infants contributes to the fetal inflammatory response without contributing to white matter damage. Our finding that M. hominis in the placenta was associated with a not quite significant threefold risk increase for echolucency deserves further investigation.