Although wide range investigations on the heart and great vessels have been reported in acromegaly, the field of microcirculation is still largely vacant. The nailfold is a window through which we can observe in vivo the vascular bed. This study investigates through nailfold capillaroscopy the morphology of cutaneous microcirculation in acromegaly in relationship with the usual hormonal parameters of disease activity. Twenty-five acromegalic patients and 26 normal subjects, age and sex matched, were studied. A subgroup of acromegalics (8 patients) was considered in stable remission, and the remaining 17 had active disease. Capillaroscopy was performed in each subject by in vivo computer aided stereomicroscopy (magnification, x400). The following morphological parameters were calculated: the number of tortuous loops, meandering capillaries, and capillaries per millimeter; avascular areas; visibility of subpapillary plexus; the capillary length; and intercapillary distance. We were unable to perform the exam in 4 of 25 patients because visibility was poor. The capillary number and length were significantly reduced in acromegalics compared to controls [8.9 +/- 1.5 vs. 10.3 +/- 1.2 no./mm (P = 0.0010) and 174 +/- 49 vs. 255 +/- 24 microm (P < 0.0001)]. Moreover, in acromegalics, the numbers of tortuous loops and meandering capillaries were significantly increased [19 +/- 8 vs. 13 +/- 5 (P = 0.0027) and 10 +/- 12 vs. 0.7 +/- 1.1 (P < 0.0001)]. The capillaroscopic alterations were still observed in a smaller group of 8 nondiabetic and nonhypertensive acromegalics. We found branch-like capillaries in 4 acromegalic patients, but not in the control group. Finally, we observed a meaningful different and ameliorated capillaroscopic morphology in acromegalic patients in stable remission compared to active disease patients as far as the total number (density) and meandering capillaries were concerned. In conclusion, our study shows that in acromegaly, morphological alterations also affect the peripheral microcirculation, which seems to be influenced by the activity of the disease. We believe that nailfold capillaroscopy may represent an additional useful tool in the follow-up of acromegalic patients.