This study assesses the initiation and duration of exclusive/almost exclusive breastfeeding (Ex/AEx-BF) versus partial breastfeeding (P-BF) and its relationship to infant growth and maternal body mass index (BMI) in Ethiopian infants up to 12 months of age (Tigray n = 471; Gonder n =596). Initiation of breastfeeding within 1 hr after birth was 1.7 times more common in Tigray. In Gonder 19% of the mothers started breastfeeding on the third day of delivery and consequently, a significant higher proportion of newborns were offered prelacteal feeds (P<0.001). At six months, 52.2% and 61.5% of mothers in Tigray and Gonder respectively practised Ex/AEx-BF. Perceived lack of breastmilk was a major factor for offering complementary foods before six months. More than 25% of infants in both regions were Ex/AEx-BF up to the eighth month and 16.4% and 15.7% of infants in Tigray and Gonder were still Ex/AEx-BF at the end of the first year. Growth faltered before six months of age but less frequently in Ex/AEx-BF compared to P-BF infants. Malnutrition became obvious after eight months in both groups. Malnourished mothers (BMI < 18.5) offering mixed feeding to their malnourished children (<-2 z-score) below six months of age was higher in both regions compared to the Ex/AEx-BF group (in Gonder 25% vs 5.9%; in Tigray 42.9% vs 33.3%). Nutrition education to raise awareness of mothers regarding initiation of exclusive breastfeeding directly after birth, the value of colostrum and avoidance of pre-postlacteal feeds, needs to be implemented. A new health package to be implemented could be a proper vehicle to reach the rural population, which doesn't have access to health services. The relationship between infant growth, mode of feeding and mothers nutritional status should be further investigated, particularly in populations with a high prevalence of maternal and infant nutrition and where long term breastfeeding is practiced.