Alvarez-Rodriguez, J., Sanz, A., Joy, M., Carrasco, S., Ripoll, G. and Teixeira, A. 2009. Development of organs and tissues in lambs raised on Spanish mountain grassland. Can. J. Anim. Sci. 89: 37-45. The present study was conducted to establish the pattern of body development in grass-raised Churra Tensina lambs. Forty-nine single male lambs were slaughtered at three body-weight intervals, according to the commercial categories of suckling (11.1 +/- 1.0 kg), light (22.1 +/- 0.8 kg) and heavy lamb (32.0 +/- 2.9 kg). Non-carcass and carcass components were recorded and the half left carcasses were completely dissected. Lambs showed a low growth rate of main organs in relation to empty body weight (BW) (P < 0.01). Skin + fleece and liver accompanied the rest of mass growth (P < 0.05). The allometric coefficients of forestomachs and large intestine were higher than that of the small intestine (P < 0.05). Joints related to locomotion had early development (P < 0.01), whereas those belonging to the trunk grew at faster rates than did carcass weight (P < 0.01). The fatty tissues has increased growth coefficients (P < 0.01), whereas bone and lean coefficients decreased (P < 0.01) with increasing carcass weight. Intermuscular fat attained greater growth rates in lambs slaughtered at light BW than in heavy lambs (P < 0.01). However, the former group displayed lower relative growth of pelvic-renal, subcutaneous and abdominal fat than the latter (P < 0.01). This trait might reflect improved investment of dietary towards deposition of adipose tissue through the increased digestive tract capacity.