Microscopy remains the gold standard for malaria diagnosis. However, quality microscopy services are severely lacking in most African countries. To improve capacity for malaria microscopy in Uganda, a 3-day refresher training program was conducted in four districts. Training impact was measured through a written examination and evaluation of the quality of blood-slide preparation and accuracy of field microscopy. A total of 184 of 192 (96%) identified laboratory personnel participated in the training. Average test scores improved from 41% to 75% (P < 0.001). A total of 1,079 and 1,190 routinely made thick blood smears were collected before and after the training, respectively. Sensitivity improved from 84% to 95% (P < 0.001), and specificity improved from 87% to 97% (P < 0.001). The proportion of well-prepared blood smears improved from 6% to 75% (P < 0.001). Supplemental training can have a significant impact on the knowledge of staff, accuracy of microscopy, and quality of blood-slide preparation.